Complex sentence: Nominally credited as an associate producer, he produced several of MGM's most important films of the 1930s and after Thalberg's death joined Paramount as a producer in 1937, where he remained until 1941.
Split into simpler sentences: Nominally credited as an associate producer, he produced several of MGM's most important films of the 1930s. After Thalberg's death joined Paramount as a producer in 1937, where he remained until 1941.