Complex sentence: Steifel agreed to manage Rod Stewart in 1983 and implemented a long term strategy to revive Stewart's then slumping career, and, by 1988, Stewart had once again ascended to superstar status.
Split into simpler sentences: Steifel agreed to manage Rod Stewart in 1983 and implemented a long term strategy to revive Stewart's then slumping career. By 1988, Stewart had once again ascended to superstar status.