While sci-fi isn't necessarily known for its sense of humor, most of the better science fiction movies and shows do incorporate laughs. More often than not, the humor comes from a supporting character with a particular charm to his/her personality. Cited here are 3 of my personal favorite sci-fi supporting characters that keep the laughs coming each time I watch!
3. Donna Noble - Doctor Who
Personally, my favorite companion from the newer seasons, Donna is brilliant and hilarious. From constantly referring to The Doctor as "spaceman" and "martian" to giving hell to unfriendly alien species, Donna was undoubtedly the funniest companion. With that humor though she also had the capacity for serious emotion, showcased beautifully in "The Fires Of Pompeii" when The Doctor insists they leave without saving anybody.
2. Walter Bishop - Fringe
Fringe is one of my favorite sci-fi shows. Aside from the cool stories and mysterious cases, there was always a humorous element embodied by Walter Bishop - the quirky-but-brilliant "mad scientist" that is struggling with his past. Sure, from that description he doesn't sound very funny, but every episode Walter says something that exposes the inner child at the heart of his character, such as, "I haven't had a root beer float in 17 years."
1. Data - Star Trek : TNG
Data is one of my favorite characters in any show. Because he is an android, he lacks certain casual interpersonal skills, like a sense of humor or sarcasm. This leads to a lot of very funny exchanges between the predominantly human crew and the only android on the ship. When we first meet Data, it is apparent that his capabilities far exceed that of humans in many respects (strength, speed, etc), though he is honest about his deep desire to be a real human himself. Throughout the course of the show, Data continues to learn about humanity, even attempting to joke and laugh at some points. "We are more alike than unlike my dear captain. I have pores. Humans have pores. I have...fingerprints. Humans have fingerprints. My chemical nutrients are like your blood. If you prick me...do I not...leak?"
All 3 of these characters were great at garnering laughs on shows that could get pretty heavy sometimes. Star Trek and Fringe are both on Netflix right now, so go and watch them if you haven't yet.