Very sad to hear this news. He had a long career, from low budget TV to dramatic roles, and then an unlikely turn later on to comedy. He was great.
Just learned the other day that Police Squad was based on an old TV show called M Squad with Lee Marvin. Lead character was even named Frank.
I had recently watched both “Police Squad” and “The Naked Gun” on DVD and they both came with an audio commentary by the writer/producers. Nielsen was signed to do Airplane! because he’d done so many serious roles (much like Peter Graves and Lloyd Bridges) and it turned out he loved being a ham. So when the Airplane! producers were looking for a lead for Police Squad, they went to Leslie who was thrilled to do more of the comedy spoof genre.
What was funny was that when the producers tried to cast The Naked Gun, the studio did not want Peter Lupus in the role of Nordberg (he was Nordberg on Police Squad) because they thought he looked too nice - more like a male model than a cop. So they suggested O.J. Simpson. The studio told the producers that Simpson “looked like someone who could be violent if he had to”. Little did they know then...
Partly based, although Nielsen's performance was inspired by the Detective Inspector (left of picture) in another 60s cop show The New Breed