Born Mikall (or Michael or Micheal) Sinnott in Richmond, in the Eastern Townships south of Montréal, Québec, his parents were Irish immigrants. His father was a blacksmith. Sennett was also a set designer and film director, producer and screenwriter who became famous for his slapstick comedies.

Oddly enough, for a man who would end up with that title, he actually started out wanting to be an opera singer. Whatever his ambitions were, his parents moved to Connecticut when he was 17 and in 1902 he was working as a common laborer. He met with vaudeville star, and fellow Canadian, Marie Dressler which led to a letter of introduction to New York producer David Belasco. Although that led nowhere, Mack stayed in New York and eventually drifted into acting.

His earliest theatrical specialty was his unique portrayal of a policeman. Sennett first acted in films at Biograph studios, playing low comedy parts. He then co-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, Raymond Griffith, Ben Turpin, Roscoe "Fatty" Arbuckle, Laurel and Hardy, Gloria Swanson, Ford Sterling, Bing Crosby, the Keystone Kops and many more.

In a very short space of time, Keystone became synonymous with screen comedy. In fact, when he left to produce independently, to be released by Paramount in 1917, he didn't fight to take the Keystone Brand with him, his own name proved more valuable.

Though Sennett occasionally experimented with color and managed to be the first to get a talkie short subject on the market in 1928, the huge overall comedown in quality really showed. The later silents and talkies were pretty poor. Though he had a popular series with up and coming star Bing Crosby, most of his stars, as always, deserted him for greener pastures.

The growth of television in the 1950's and the need for quick, inexpensive programs brought many of his films back from near obscurity. A whole new generation of people discovered the magic of the Keystone Kops and the silent era. Sennett enjoyed a brief spell of fame and popularity but it was now very late in his life.

Today his name is still highly recognizable, even to those who will have virtually no contact with his films, and the term "Keystone Kops" has become part of the language to describe incompetent buffoons with some supposed authority. He died, a few months short of his 81st birthday, in Woodland Hills, California and was interred in the Holy Cross Cemetery in Culver City, California.

Was Mack Sennett gay? He got a mention by D.W. Griffith's first wife and memoir writer Linda Arvidson - "We wondered about Mack Sennett. Would he ever buy a girl an ice-cream soda?" - an implication perhaps seconded by the actor Ralph Graves, who told historian Anthony Slide he'd had an "unholy relationship" with the king of silent comedy.

From: Mann, W.J. Behind the Screen: How Gays and Lesbiand Shaped Hollywood. Penguin, 2001. p. 11

Source: http://www.4reference.net/encyclopedias/wikipedia/Mack_Sennett.html - et alii