Simplify the following text for a Grade 9 native English-speaking person.
Original: In addition to his work with Asimov 's ( which he also co-founded in 1976 ) , he also worked in the 1970s with magazines such as Galaxy Science Fiction , If , Worlds of Fantasy , and Worlds of Tomorrow .
Simplified: He also worked in the 1970s with magazines such as Galaxy Science Fiction , If , Worlds of Fantasy , and Worlds of Tomorrow .