Complex sentence: Zachary Quinto, who had a recurring role as Chad in the first season, was confirmed as one of the leads in March 2012, portraying Dr. Oliver Thredson, a psychiatrist with groundbreaking treatment methods that go against Sister Jude's.
Split into simpler sentences: Zachary Quinto, who had a recurring role as Chad in the first season, was confirmed as one of the leads in March 2012. He portrayed Dr. Oliver Thredson, a psychiatrist with groundbreaking treatment methods that go against Sister Jude's.