Full disclosure: the majority of the intelligence in this post comes from Brent Walker’s indispensable reference Mack Sennett’s Fun Factory. Only with great restraint do I not spill all the cool details Walker pulled together; for that you must buy his book, which no serious silent comedy fan would ever regret doing. NOTE WELL: the IMDB entry for this performer appears to conflate him with the son of Broadway mogul Henry Miller. Henry Miller Jr also appeared in silent films at around the same time, but I am convinced they are two different men.
Our Rube Miller (Harry Carl Miller, 1887-1944) was born in Trottwood, Ohio and was an aerial circus performer with Ringling Brothers from age six. He was one of the boss clowns with Forepaugh and Sells for a number of years before getting his foot in the door at Mack Sennett’s Keystone in 1913 as a bit player in a ton of crude comedy classics of their kind: A Deaf Burglar (1913), Bangville Police (1913), Their First Execution (1913), Toplitsky and Company (1913), Barney Oldfield’s Race for a Life (1913), A Muddy Romance (1913), The Gusher (1913), A Thief Catcher (1914), Tango Tangle (1914), His Favorite Pastime (1914), A Star Boarder (1914), The Knockout (1914), and Tillie’s Punctured Romance (1914), supporting such greats and near-greats as Fred Mace, Ford Sterling, Charlie Chaplin, and Mabel Normand. In 1915 and ’16 he starred in some of his own comedies for Vogue, sometimes co-starring with Ben Turpin. He directed some Ham and Bud shorts during the same period. He directed and acted at L-KO, as well. A small role in the Lloyd Hamilton short Twilight Baby (late 1919) appears to be his last on-camera credit. All told he directed 63 films and performed in around 100. In the 1920s and ’30s he appears to have returned to his circus origins as a clown and slack-wire artist. He died in 1944 (not 1927, as IMDB tells us. That would be the other Henry Miller).
For still more on silent film and classic comedy, please read Chain of Fools: Silent Comedy and Its Legacies from Nickelodeons to Youtube,