Mathematician:Thales of Miletus

Greek mathematician, scientist, philosopher and astronomer, who (amongst other things) predicted a solar eclipse in 585 B.C.E.

Nationality
Greek

History

 * Born: c. 625 B.C.E.
 * Died: c. 547 B.C.E.

Theorems and Definitions
The following are attributed to Thales:
 * A circle is bisected by any diameter.
 * The base angles of an isosceles triangle are equal.
 * The vertical angles formed by two intersecting straight lines are equal.
 * A triangle is completely determined if two angles and the included side are given.
 * An angle inscribed in a semicircle is a right angle.

All of the above are found in "The Elements" by Euclid.