Yuri Gagarin became the first man in space on April 12, 1961.

From Funk & Wagnalls -
After graduating from technical and vocational schools, he enrolled at the Soviet air force cadet training center at Orenburg, graduating as a pilot in 1957. On April 12, 1961, Gagarin, then a major in the air force, became the first man to travel in space when he rode aboard the earth satellite Vostok (later referred to as Vostok 1) on a 27,400 km/hr (17,000 mph) single orbit of the earth. The flight lasted 1 hr 48 min, on an elliptical course having an apogee of 327 km (203 mi) and a perigee of 180 km (112 mi). He was killed in the crash of a test airplane.

Read more about the history of manned space flight.