William Bennett Kilpack (February 6, 1883 in Long Melford – August 17, 1962 in Santa Monica) known simply as Bennett Kilpack, was an actor, director and playwright. He is best known for his performances in the title role of Mr. Keen, Tracer of Lost Persons (from 1937–1947 on NBC Radio's Blue Network, which became the ABC network in 1945, then from 1947 to 1955 on CBS Radio). The drama was one of radio's longest running Old-Time Radio shows (October 12, 1937 to April 19, 1955), continuing well into the television era. He toured with Sir Philip Ben Greet's Shakespearean players, had several important parts in Broadway plays, and in 1927 was given the lead role in The Wayside Inn, an early radio serial. He subsequently played the part of Cephus in Way Back Home, which was presented on radio and as a film, with Phillips Lord as Seth Parker. As a radio serial it was also known as Sunday Night at Seth Parker's. Kilpack made his CBS debut in 1935 in Vanished Voices and subsequently played roles on CBS Radio in Hilltop House, Gang Busters, The Goldbergs, The Shadow and Grand Central Station.

Kilpack began his run as Mr. Keen in 1937. For 18 years Keen and his faithful assistant, Mike Clancy, entertained followers with their intuitive perception that kept listeners coming back for more. With 1690 nationwide broadcasts, Mr. Keen was the most resilient private detective in a namesake role. The nearest competitors were Nick Carter, Master Detective (726 broadcasts), The Adventures of Sherlock Holmes (657) and The Adventures of the Falcon Over a span of 13 years, Bennett appeared on nearly 1300 of the 1690 broadcasts. At age 67, Bennett made his last appearance as Mr. Keen on October 26, 1950, the show's 1314th broadcast.