An unassuming screenwriter and actor, Mr. Henry thought up quirky characters with Mel Brooks and inhabited many more on “Saturday Night Live.” Buck Henry, a writer and actor who exerted an often overlooked but potent influence on television and movie comedy — creating the loopy prime-time spy spoof “Get Smart” with Mel Brooks, writing the script for Mike Nichols’s landmark social satire “The Graduate” and teaming up with John Belushi in the famous samurai sketches on “Saturday Night Live” — died on Wednesday in Los Angeles. He was 89. A friend, Dianne V. Lawrence, said Mr. Henry’s wife, Irene Ramp,...