Simplify the following text for a Grade 5 native English-speaking person.
Original: Pretoria itself was founded in 1855 by Marthinus Pretorius , a leader of the Voortrekkers , who named it after his father Andries Pretorius .
Simplified: Pretoria itself was founded in 1855 by Marthinus Pretorius . He was a leader of the Voortrekkers .