Nielsen was a serious dramatic actor. He was Captain of the SS Poseidon in the first make of the Poseidon Adventure, a seriously good drama. Every respectable woman I know rolls their eyes when Airplane or Naked Gun movies comes on, but I can watch those movies and laugh until tears flow. Nielsen was seriously funny. I'll swear he had the same serious look in Airplane as he did in the Poseidon adventure when he said "I am serious, and don't call me Shirley."
Forbidden Planet is on the list of the best 50's sci-fi movies, it was really well made. If you haven't seen it, I recommend it. And we all loved him in the Naked Gun and Airplane comedies. RIP to a great entertainer.