Thales Of Miletus

Thales of Miletus (about 624BC - about 547BC) is considered one of the first mathematicians and philosophers, if not the first, although his occupation was that of engineer. Certainly he is renowned as one of the legendary Seven Wise Men of antiquity.

The idea that he was a professional engineer should be taken with a heavy dose of salt, especially since the distinction between mathematicians, philosophers, and engineers scarcely existed at that point.

As with most figures from that time it's difficult to say exactly what he did and did not do or write since so little survives, but several theorems are attributed to him, as are the seeds of GeekFu. He reputedly correctly predicted a solar eclipse, and is allegedly the first to have done so.

Thales Theorem:

The inscribed angle in a semi-circle is a right angle.
A diameter of a circle subtends 90 degrees from any point on the circumference.