He was 84, so we knew his time would come eventually, but due to complications from penumonia, Lt. Frank Drebin will not be back for a Naked Gun 4.
He was generally a straight man through most of his career (Forbidden Planet), but it was 1980's Airplane! where deadpan skills really came out. That led to the short-lived Police Squad, and then the Naked Gun trilogy.
And yet, I'll also never forget him as Barbra Streisand's would-be assailant in 1987's Nuts. That was not a role he would have ever been offered if The naked Gun had already come out.