Hans was a SPECTRE operative who served as Ernst Stavro Blofeld's personal bodyguard in his Japanese volcano lair. He was a tall, blonde, possibly German man dressed entirely in black who never spoke. In addition to serving as Blofeld's bodyguard, Hans also looked after the piranhas in Blofeld's office, keeping them regularly fed with hunks of meet on the end of a chain.
During SPECTRE's plan to start a war between the United States and the Soviet Union, Hans was given the key to operate the remote self-destruct mechanism for SPECTRE's rocket ship which was kidnapping American and Russian spaceships. Blofeld intended to destroy his own rocket ship following the theft of the third ship, so as to eliminate evidence of SPECTRE's involvement.
When Japanese agents led by Tiger Tanaka arrived to assist James Bond, Blofeld fled, but Hans remained behind to destroy the SPECTRE rocket after it took the American one. Bond however wanted to destroy it before it captured its prey, to save the American astronauts. He fought his way up to Blofeld's office where Hans barred his way. The two men fought. The bigger Hans initially had the upper hand, but Bond managed to get the key from Hans' pocket and ran towards the control room.
Hans chased him and the fight resumed on the bridge which spanned the indoor pond containing the piranhas. Bond ducked Hans' punch, and Hans' momentum made him fall onto Bond's back, and he then flipped the SPECTRE henchmen head over heels off of the bridge and into the pond, where he was immediately devoured by the piranhas.