Nikolai Lobachevsky

Nikolai Lobachevsky (1792–1856) was a Russian mathematician known primarily for his contributions to geometry, particularly for developing the concept of non-Euclidean geometry. He is often referred to as the "father of non-Euclidean geometry." Lobachevsky challenged the long-held assumption in Euclidean geometry that through any point not on a given line, there is exactly one line parallel to the given line.