In his youth he always carried a copy of Disquestiones Arithmaticae with him. Along with Legendre he gave the first proof of Fermat's Last theorem in the case of n equals 5. For his corrections of Cauchy, he is credited with 
In his youth he always carried a copy of Disquestiones Arithmaticae with him. Along with Legendre he gave the first proof of Fermat's Last theorem in the case of n equals 5. For his corrections of Cauchy, he is credited with developing the field of Fourier analysis. In 1837, he developed the modern definition of a function. FTP, name this successor to Gauss at G?ttingen whose name is also sometimes given in association with the pigeonhole principle and whose namesake theorem deals with primes in arithmetic progression.
In his youth he always carried a copy of Disquestiones Arithmaticae with him.
Peter Gustav Lejeune Dirichlet