Today, we celebrate people with the name Boris. But isn't it ironic that the most famous Boris of all is actually called... William?! Boris Karloff, whom we all know for his portrayal of Frankenstein's monster in the first three Universal movies, was born William Henry Pratt in 1887, and there was nothing russian about him. A bit indian on his paternal grandmother's side, but no reason for him to choose Boris Karloff as his stage name.
Before he became an icon of horror, he was an intimidating supporting actor in stage plays and a truckload of silent films. He was already 32 when he first appeared on screen. Finding these early performances can be a bit tricky, but you should be able to find a copy of Tarzan and the Golden Lion (1927) somewhere.
In 1931, James Whale directed a lavish screen version of Frankenstein, which was not adapted from the book but from a successful stage play. The scientist was played by Colin Clive, but the creature was embodied by an mysterious uncredited actor, whose name was only revealed in the closing credits. Boris Karloff became a star overnight, and returned of course in The Bride of Frankenstein (1935), Son of Frankenstein with Basil Rathbone and Bela Lugosi (1939), House of Frankenstein (1944, where Karloff didn't play the monster but a Dr Gustav Niemann), but also played Fu Manchu, Mr Wong (a Fu Manchu ripoff), the Mummy Imhotep, various mad scientists and a bunch of villains who antagonize Dick Tracy and Charlie Chan.
In 1953, the golden age of black & white horror was almost over, and Karloff only played Dr Jekyll and Mr Hyde for laughs, opposite Abbott & Costello. In 1958, at a time where Hammer Films was taking over gothic horror, he played Baron Frankenstein himself in a weak movie called Frankenstein 1970, where he used body parts from a film crew to create his monster.
In the 60s, he became mostly a guest star in TV shows like I Spy and The Wild Wild West, but he also returned to Frankenstein in a weird little movie called Mad Monster Party, where he provided the voice of Baron Boris von Frankenstein (!)
Boris Karloff died in 1971, but he's very fondly remembered by classic horror fans, along with Bela Lugosi and Lon Chaney Jr. However, it seems that these three never shared the same bond as their successors Peter Cushing, Christopher Lee and Vincent Price.
Boris is the name of the dog in Sherlock Holmes vs Frankenstein, and I admit to it being a not-so-subtle wink to Karloff!