The Golem (real name Oscar Dzundza) is an antagonist who appears in the Sherlock episode "The Great Game". He is a Czechoslovakian contract assassin hired by James Moriarty.
The Golem is an extremely dangerous assassin. He is sadistic as he laughs when John Watson threatens to shoot him, and again when he attempts to strangle Watson himself. He has no qualms about who he kills or how much agony he causes his victims, only, it seems, that he gets the job done. It is unknown what happened to the Golem after Moriarty's death, but it can be assumed that he moved on. He possesses near-superhuman strength.
Oscar's modus operandi is strangling. He squeezes the life out of his victims with his bare hands. He is surprisingly agile for his size and is seen kicking a handgun out of Watson's hand. He is a formidable hand to hand combatant and was easily able to overpower Sherlock Holmes and John Watson in a short battle.
Oscar is hired to kill Alex Woodbridge, a security guard working for an art museum called the Hickman Gallery. An amateur astronomer, Woodbridge had realised that one of the paintings at the museum, supposedly an original Vermeer, was a fake. Woodbridge's corpse is discovered by Greg Lestrade and his team near the Thames. Sherlock, after some research, recognises the Golem's trademark kill. He uses his "Homeless Network" to discover his location in Vauxhall, where he has been sleeping rough. Before he and Watson can confront Oscar, however, Dzundza attacks them with the element of surprise and, whilst being held at gunpoint by John Watson, tries to suffocate Sherlock. The Golem changes tactics and then attacks Watson. A complicated standoff breaks out and the Golem retreats. They pursue him to an astronomy research centre, where he kills Professor Cairns, who had corresponded with Woodbridge about the possibility of the painting being a fake. A violent struggle ensues. Sherlock tries and fails to shoot Oscar, who escapes.