Complex sentence: Carnovsky's Shylock was a huge hit, no doubt helped by the fact that his co-star was Katherine Hepburn, who played Portia, but even Ms. Hepburn couldn't upstage Carnovsky's brilliant portrayal of Shylock.
Split into simpler sentences: Carnovsky's Shylock was a huge hit, no doubt helped along by the fact that his co-star was Katherine Hepburn, who played Portia. But even Ms. Hepburn couldn't upstage Carnovsky's brilliant portrayal of Shylock.