David Zucker, one end of ZAZ, tells the story of The Man Who Would Be Dr. Rumack:
At our first meeting, he mentioned proudly that he had done an episode of M*A*S*H.
We assured him we wouldn’t count this brief comedy experience against him. But when he read the Airplane! script he “got” its unconventional nature and off-beat style. We heard later that he told his agent, “Take whatever they offer, I’d pay them to do this.” Arguably the best role was that of Dr. Rumack, played by the guy no one wanted or ever suspected would be funny, much less go on to have a second career starring in feature films as a goof-ball comic. Leslie was great in the role because he never “winked” — let on that he knew he was in a comedy. This was essential to the style, and Leslie had a natural instinct for it.
Which instinct, of course, led directly to Sergeant Frank Drebin, Detective Lieutenant, Police Squad, and occasional locksmith.