Complex sentence: He was the main songwriter (Clint Mansell also wrote) and drummer until the release of "Box Frenzy" in 1987, after which he took on full vocal duties and became co-frontman with Mansell.
Split into simpler sentences: He was the main songwriter (Clint Mansell also wrote) and drummer until the release of "Box Frenzy" in 1987. After which he took on full vocal duties and became co-frontman with Mansell.