Simplify the following text for a Grade 6 native English-speaking person.
Original: Sir Martin John Evans ( b. 1 January 1941 , Stroud , Gloucestershire ) is a British scientist who , with Matthew Kaufman , was the first to culture mice embryonic stem cells and cultivate them in a laboratory in 1981 .
Simplified: His first success was with Matthew Kaufman . In 1981 they were the first to grow embryonic mice stem cells in a laboratory .