The Outer Limits 1963 s2 e 13 The Duplicate Man

It is the year 2025; fourteen years previously wealthy research academic Henderson James had Captain Karl Emmet smuggle a Megasoid to Earth.[1] It is illegal to possess a Megasoid as they are highly dangerous, always thinking about killing, unless in a reproductive cycle, which this one now is. When the Megasoid escapes to hide amongst the stuffed exhibits at a nearby space zoo, James, lacking the courage to track it down and kill it himself, has a clone of himself illegally made for the purpose by clone bootlegger Basil Jerichau. Strict guidelines govern the production of these "duplicates", which must be destroyed before vestigial memory renders them indistinguishable from the originals.

The clone botches its mission at the zoo and the Megasoid gets away after informing the clone that he is a duplicate. A trace of memory leads the duplicate James to the home of Captain Emmet. Emmet panics and tries to phone the police; the duplicate James knocks him out cold; and, accumulating more of the real Henderson James’ memories as he goes, he finds his way to "his" own home. The wounded Megasoid returns to the James home and hides in the bushes. Duplicate James meets the real James’ wife, Laura, who sees in him a more youthful version of her husband before he became obsessed with studying the Megasoid. The real James has gone to bribe Emmet into killing the duplicate James once he has completed his mission. Returning home, he leaves Emmett on the grounds to await duplicate James’ arrival. Unfortunately, Emmett is attacked and killed by the Megasoid. Entering his home, the real James meets his duplicate. Seeing a more compassionate version of himself gives him the courage to kill the alien, as he believes Laura would be happier with the duplicate.

Henderson James and his duplicate hunt for the Megasoid. James shoots the alien after it has torn his duplicate apart. He discovers that his clone was dying all the time, from a timed release of poison into his blood stream; a precaution provided by the clone bootlegger. A less cynical Henderson James is now reconciled with his wife.