Complex sentence: Steiger read extensively about Fields in preparation for the role, and developed an encyclopaedic knowledge of his career and personal life, and concluded that he would base his characterization around his performance in "The Bank Dick" (1940).
Split into simpler sentences: Steiger read extensively about Fields in preparation for the role, and developed an encyclopaedic knowledge of his career and personal life. He concluded that he would base his characterization around his performance in "The Bank Dick" (1940).