Simplify the following text for a Grade 8 native English-speaking person.
Original: Saleh previously served as President of the Yemen Arab Republic ( North Yemen ) from 1978 until 1990 , at which time he assumed the office of chairman of the Presidential Council of the Republic of Yemen ( unified Yemen ) .
Simplified: Before that time , Saleh served as the President of the Yemen Arab Republic ( North Yemen ) from 1978 until 1990 . In 1990 , he assumed the office of chairman of the Presidential Council of the Republic of Yemen ( North & South Yemen ) .