The Leslie Triplets were a special team aboard the original USS Enterprise consisting of three twin brothers, all of them usually called "Leslie" and serving in different divisions.
Another Mr. Leslie served on the bridge, usually as an engineer, but he also controlled the helm sometimes. Once he mutinied against Captain Kirk while being controlled by alien spores which made Mr. Spock climb a tree and shout "I want a woman!" (Err... no... the latter was in some old Italian flick...). The same Leslie uttered the now legendary words: "We're leaving orbit, sir." after some blonde, Shakespearian actress chick killed her father while performing "Hamlet". Spock always confused this Leslie with Yeoman Janice Rand, probably because they shared the same curvaceous hips (TOS: "Take Over Here, Rand").
The third Leslie was a medical technician. Because he had enough of fellow officers mistaking him with his brothers he changed his name to the much more cooler "Connors". He was a notorious womanizer, mostly specializing in dark-haired babes in green dress. (TOS: "Why Is a Green Shirt Working in Sickbay?").
In 2268 some evil alien Nazis cloned Mr. Leslie and used him as a Wehrmacht soldier. The clone also had a silly-looking mustache.
- Some fans can assume that actually there were only one "Mr. Leslie" but that wouldn't explain his presence in multiple places at the same time.