Mack Sennett is the inventor of the slapstick comedy. He was a singer, dancer, clown, actor, set designer and director for Biograph, and founded Keystone in 1912 together with Adam Kessel. Many important actors were discovered by him and started their career at Keystone. Those include
Charlie Chaplin, [Ben Turpin]
?, [Fatty Arbuckle]
?, [Laurel and Hardy]
?, [Gloria Swanson]
? and many more.