Complex sentence: Jekyll's motives for experimenting with the potion, which were ambiguous in Stevenson's story, were made more clearly benign by Sullivan, whose Jekyll tells Lanyon that his discovery will "benefit the world".
Split into simpler sentences: Jekyll's motives for experimenting with the potion, which were ambiguous in Stevenson's story, were made more clearly benign by Sullivan. Sullivan's Jekyll tells Lanyon that his discovery will "benefit the world".