when  who  what 

1900 BC  Babylonians  A clay tablet, now in the museum of Columbia University, called Plimpton 322, contains 15 triples of numbers. They show that a square can be written as the sum of two smaller squares, e.g., 5^{2} = 3^{2} + 4^{2}. 
circa 530  Pythagoras 
Pythagoras
was born in Samos. Later he spent
13 years in Babylon, and probably learned the
Babylonian's results, now known as the Pythagorean triples. Pythagoras was also the founder of a secret society that studied among others "perfect" numbers. A perfect number is one that is the sum of its multiplicative factors. For instance, 6 is a perfect number (6 = 1 + 2 + 3). Pythagoreans also recognized that 2 is an irrational number. 
circa 300 BC  Euclid of Alexandria  Euclid is best known for his treatise Elements. 
circa 400 BC  Eudoxus  Eudoxus was born in Cnidos, and became a colleague of Plato. He contributed to the theory of proportions, and invented the "method of exhaustion." This is the same method employed in integral calculus. 
circa 250 AD  Diophantus of Alexandria  Diophantus wrote Arithmetica, a collection of 130 problems giving numerical solutions, which included the Diophantine equations, equations which allow only integer solutions (e.g, ax + by = c, x^{2}  Dy^{2} = 1, x^{3} + y^{3} = z^{3}, etc.). Of 13 volumes only six survived and the rest were destroyed in the fire that burned the library of Alexandria. The copy Fermat had was the one translated by Claude Bachet in 1621. Diophantus' Problem 8 in Volume II asks how to divide a given square number into the sum of two smaller squares. Subsequently, this problem inspired Fermat to write his famous Last Theorem. 
830  AlKhowarizmi  Abu Ja'far Mohammed ibn Mûsâ alKhowârizmî (Father of Ja'far, Mohammed, son of Moses, native of the town of AlKhowârizmî), a Persian author, had written a book which included the rules of arithmetic, called Kitab al jabr w'almuqabala (Rules of restoration and reduction) dating from about 825 AD. From the title of this book we derive our modern word algebra. 
1225  Fibonacci (or Leonardo) of Pisa 
Leonardo
(11801250) grew up in North Africa under the Moors and later travelled extensively
around the Mediterranean coast.
He recognized the advantages of the "HinduArabic" system. He is best known for the
sequence, the Fibonacci
Numbers, which appear in a book he wrote, Liber Abaci. In this
sequence each term after the first is obtained by adding together the two preceding
numbers: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, ... The ratio of two successive numbers in the sequence: 1/1, 1/2, 2/3, 3/5, 8/13, 13/21, 21/34, 34/55, 55/89, 89/144, 144/233, ... tends to (5  1)/2, which is called the Golden Section. 
early 1500s  The Cossists  The Arabs called the unknown quantity shai (thing), which is cosa in Italian. These Italian algebraists came to be known as the Cossists (Aczel). Well known Cossists included Geronimo Cardano (15011576) and Niccolo Tartaglia (15001557). 
early 1600s  Claude Bachet  Bachet acquired a copy of the Greek Arithmetica of Diophantus, and translated and published it as Diophanti Alexandrini Arithmeticorum Libri Sex in Paris in 1621. 
circa 1637  Pierre de Fermat 
The French jurist, Fermat
(16011665), studied Viéte's unpublished writings
and studied them carefully. van Schooten published Viéte's Opera
Mathematica in 1646. Fermat moved to Paris in 1636 and formed a scientific circle around Father Mersenne and Etienne Pascal. Some of his correspondence with this group has been preserved. Fermat published anonymously a dissertation on the rectification of curves Lalouvé published in 1660 as an appendix to his book on the cycloid. J. E. Hoffmann in 1943 also discovered 8 anonymous pages appended to a copy of Frenicle's rare pamphlet of 1657 on Pell's equation and other topics. Fermat pondered publication of his work on a few occasions, but he insisted on anonymity because the amount of supervision required to produce an adequate copy. Fermat's Last Theorem (FLT) states that n^{th} power of a positive integer cannot be expressed as the sum of n^{th} powers of two smaller positive integers, where n > 2, i.e., there are no positive integers x, y, and z such that
Fermat proved his Last Theorem for n = 4, using the method called "infinite descent" to prove that there are no positive integers, a, b, and c such that a^{4} + b^{4} = c^{4}. Moreover, if a solution exists for some n, the same solution also works for any multiple of n. Hence, only prime numbers have to be considered. Fermat also proved the theorem for n = 3. 
Leonhard Euler (17071783)  Euler proved FLT for n = 3 and 4 independently. Euler invented the imaginary number, i, and created a new field, topology.  
1801  Carl Friedrich Gauss (17771855)  Gauss was born in Brunswick, Germany, and he found no fellow mathematical collaborators and worked alone for most of his life. Gauss published Disquisitiones Arithmeticae. Gauss studied the behavior of functions on the complex plane. Some of these analytic functions, called modular forms, turned out to be crucial to the new approaches to the FLT. 
Sophie Germain (17761831)  Sophie Germain assumed a man's name, Mr. Leblanc. Sophie Germain's theorem states that if a solution of Fermat's equation for n = 5 existed, all three numbers must be divisible by 5. The theorem divides FLT into two cases: Case I for numbers that are not divisible by 5, and Case II for numbers that are.  
1828  Peter G. L. Dirichlet  Dirichlet proved FLT for n = 5, and 14 (1832). He also proposed a modern definition of functions. 
1840  Gabriel Lamé and Henri Lebesque  They proved the FLT for the case n = 7. 
Joseph Fourier (17681830)  In his research on heat, Fourier developed the theory of periodic functions. Such a series is called a Fourier Series. He discovered that most functions can be estimated to any degree of accuracy by the sum of many sine and cosine functions. Subsequently, Fourier series plays an important role as the tool for transforming mathematical elements from one area to another in the work of Goro Shimura.  
1839, 1847  Gabriel Lamé (17951870)  Lamé proved FLT for n = 7 in 1839. Subsequently, he suggested a general approach to the problem and factored the left side of Fermat's equation, x^{n} + y^{n}, into linear factors using complex numbers, but the factorization he suggested was not unique, and hence there was no solution. 
Ernst Eduard Kummer (18101893)  Kummer attempted to restore the uniqueness of factorization by introducing 'ideal' numbers. Kummer proved that FLT was true for an infinite number of exponents, those that are divisible by "regular" primes. As a result, FLT was known to be true for all exponents less than 100.  
1825, 1829  Janos Bolyai (18021860) Ivanovitch Lobachevsky (17931856) 
Bolyai developed nonEuclidean geometry. He published his strange new world as a 24 page appendix to his father's book. Lobachevsky published a similar work. 
1846  Évariste Galois (18111831)  Galois is known for his contributions to group theory. He produced a method of determining when a general equation could be solved by radicals. He jotted down his theory the night before his duel and his paper was sent to his friend Auguste Chevalier. Joseph Liouville published his work in 1846. 
1824  Niels Henrik Abel (18021829)  In 1824 Abel gave the first accepted proof of the insolubility of the quintic. Abelian group is a crucial element in the modern treatment of the Fermat problem. It is a group where the order of mathematical operations can be reversed without affecting the outcome. 
Richard Dedekind (18311916)  Dedekind introduced the notion of an ideal which is fundamental to ring theory. Subsequently, ideals were destined to inspire Barry Mazur, and Andrew Wiles would utilize Mazur's work.  
Henri Poincaré (18541912) 
It is said that
Poincaré was the originator of algebraic topology. He elevated the status of
topology with his publication of
Analysis Situs. He studied periodic functions in the complex plane. These
were functions that remained unchanged when the complex variable z was changed
according to f(z) —> f(az+b/cz+d), and (a,b,c,d) arranged as a matrix formed an
algebraic group. These were called automorphic forms. Poincaré then extended them to modular forms. These modular forms reside on the upper half of the complex plane with a hyperbolic geometry. In this space, the nonEuclidean geometry of Bolyai and Lobachevsky rules and Euclid's fifth postulate does not hold (which states that given a line and a point not on the line, a unique line can be drawn through the point parallel to the given line.) 

1922  Louis J. Mordell 
Mordell
discovered the connection between the solutions of algebraic equations and
topology. Twodimensional surfaces in threedimensional space can be classified according to their genus, which is the number of holes in the surface. For example, the genus of a doughnut or a (wedding) ring is one. If the surface of solutions had two or more holes, then the equations had only finitely many whole number solutions, and this came to be known as Mordell's conjecture. 
1955  Yutaka Taniyama (19271958) Goro Shimura 
Taniyama
and Shimura helped organize the TokyoNikko Symposium on Algebraic
Number Theory. André accepted the invitation to attend the symposium. Jean
Pierre Serre also attended. Taniyama's problem constituted a conjecture about zeta
functions. He seemed to connect Poincaré's automorphic functions of the complex
plane with the zeta function of an elliptic curve. It was an intuition, a gut feeling that the
automorphic functions with symmetries on the complex plane were somehow connected
with the equations of Diophantus. Taniyama suggested that automorphic functions are associated with the elliptic curves, whereas Weil did not believe that there was such a connection in general. 
early 1960s  Goro Shimura 
Shimura conjectured that every elliptic curve over the rational numbers is uniformized
by a modular form. Shimura declared his conjecture that an elliptic curve should always be
uniformized by a modular curve, but André Weil did not believe Shimura
conjecture. The conjecture became misquoted as WeilTaniyama conjecture instead of Shimura Taniyama conjecture. Weil showed reluctance to refer to Shimura. Even in 1967, in a paper written in German, Weil did not attribute the theory to its originator, Shimura.

early 1970s  André Weil  Since Weil had written about the conjecture, modular elliptic curves became know as "Weil curves." After Taniyama's problems became known in the West, the conjecture came to be called erroneously the "TaniyamaWeil" conjecture, and Shimura's name was left out. According to Aczel, even in 1979, Weil spoke against the 'Mordell conjecture' on Diophantine equations. 
1977  Barry Mazur  Mazur's paper on the Eisenstein Ideal suggests that it is possible to switch from one set of elliptic curves to another. This paper implies, for instance, that it is possible to transform a problem with elliptic curves based on the prime number 3 to another using the prime number 5. 
1983  Gerd Faltings 
Faltings
proved the Mordell conjecture. Since the genus of the Fermat equation for n
> 3 was 2 or more, it became evident that the integer solutions to the Fermat equation
were
finite, if they existed at all. Granville and HeathBrown further showed that the number of
solutions of Fermat's equation, if they existed, decreased at the exponent n increased. The theorem was proved for n up to a million in 1983. For larger n, the solutions were very few and decreasing with n, if they existed at all (Aczel). 
1984  Gerhard Frey 
Frey gave a talk at a number theory conference in Oberwolfach. His paper seemed to imply
that if the ShimuraTaniyama conjecture were true, FLT would be
proved. Frey's reasoning: Suppose that Fermat's Last Theorem is not true. Then for some power n > 2, there is an integer solution to Fermat's equation, (x,y,z) = (a,b,c). This particular solution results in a specific elliptic curve, now called Frey curve, was very strange, and definitely not modular. However, if ShimuraTaniyama conjecture were true, an elliptic curve that was not modular could not exist. Thus, Frey's curve, an elliptic curve that was not modular could not exist, and hence the solutions to Fermat's equation could not exist either. This is called the Frey conjecture. (Aczel, 1996, p. 112) 
1985  Kenneth Ribet  Ribet proved a theorem that establishes that if the ShimuraTaniyama conjecture was true, FLT necessarily follows as a direct consequence. However, the ShimuraTaniyama conjecture must be proved. 
1987  Andrew Wiles 
Wiles
tried to show that the number of elliptic curves and that of
modular elliptic curves are the same. He limited
the ShimuraTaniyama conjecture to the case of semistable elliptic curves with
rational numbers as coefficients. Wiles then tried to count sets of Galois representations
associated with the semistable elliptic curves, thereby showing that they and modular
forms are the same. In 1993, with the help of Nick Katz, Wiles began to teach a course "Calculations with Elliptic Curves." 
1993  Andrew Wiles  Wiles had already proved that elliptic curves based on five were modular. Wiles wrote up 200 pages to prove FLT. Wiles also worried about the refereeing process in journals, and presented it at a conference. The paper was sent to a number of leading experts. 
1993  Nick Katz  Katz found a flaw in the proof; there were no Euler System. 
1993  Richard Taylor  Taylor, a former student of Wiles, joined him to salvage the proof. 
1993  Andrew Wiles  Wiles wrote up his proof using the corrected Horizontal Iwasawa Theory approach. 
1995  Andrew Wiles  May 1995 issue of the Annals of Mathematics published Wiles' original Cambridge paper and the correction by Taylor and Wiles. 
References
Amir D. Aczel, Fermat's Last Theorem: Unlocking the Secret of Ancient
Mathematical Problem, Four
Walls Eight Windows, New York, October 1996. (a
delightful book!)
E. Kwan Choi, "Fermat's
Last
Theorem—Was It a Right Question?", October 1998.
Alex LopezOrtiz, Fermat's Last
Theorem, February 20, 1998.
MacTutor History of Mathematics Archive, Fermat's Last Theorem.
Alf van der Poorten, Notes on Fermat's Last Theorem, Canadian
Mathematical Society Series of Monographs and Advanced Texts, John Wiley & Sons, Inc.,
New York, 1995.
André Weil, Number Theory, An approach through history, From
Hammurapi to
Legendre, Birkhäuser, Boston, 1983.
Acknowledgment
Some statements are quoted from Amir D. Aczel, Fermat's Last Theorem,
© Four Walls Eight Windows, permission to quote from Four Walls Eight
Windows.