Pythagoras
disability: epilepsy (source)
Most famous is his
theory for working out the
length of sides on a right-angled triangle; namely:
"the square on the hypoteneuse
(the longest side) is equal to the sum of the squares on the other
two sides".
Less well-known is
Pythagoras' second theory, which can be used for a non-right angled
triangle.
This has many uses, including
triangulation
(which also has many uses,
including use by the DTI for tracking down and raiding pirate radio
stations - b******s!)