Mathematics was his pass-time.
Many mathematicians disliked him for his teasing.
The mischievous mathematician would often develop a new theorem, construct a proof, and then issue a challenge to other mathematicians to prove his theorems. Fermat's game playing often made him a nuisance to other mathematicians who did not appreciate his methods. It was common for Fermat to announce a proof of some idea and not show the proof to anyone, perhaps receiving some sort of glee from the ability to stump other geniuses. (Simon Singh)
Contribution