Donald Duck may disagree, but I did exist, even though no record exists as to my dates of birth or death.
Many, many centuries after my death, Fermat would generalize my famous theorem...a generalization that was not proven until Wiles entered the scene even much later.
After being held prisoner in Babylon, I escaped to Crete and founded a school called the "semicircle."
Later, I founded a philosophical, religious school in Croton, with an inner circle of followers known as mathematikoi who lived permanently with the school, had no personal possessions, were vegetarians, and obeyed strict rules.
My followers and I believed that everything was number.
If you do not know who I am but do know about the square root of 2, then I suggest you never set sail on a ship with my followers!
Pythagoras (circa 569 B.C. - 475 B.C.)