Because you like Jenny Flint in Doctor Who
Sam Montgomery works hard, but her evil stepmother makes sure her efforts don't pay off. See them in A Cinderella Story.
Frodo might have carried the ring, but Samwise Gamgee carried the ring bearer. See them in The Lord of the Rings.
Charlie Bucket may be down-on-his-luck, but his spirits are always sky high. See them in Charlie and the Chocolate Factory.
Wanderer is a Soul, a parasite sent into a host to take over their body, extracting information from them and colonizing their species. See them in The Host.
Caleb Rivers is a bad boy with a good reason for acting out. See them in Pretty Little Liars.
A karate master/rocket scientist/squirrel, Sandy Cheeks is the only one who can clean up the other resident's messes in Bikini Bottom. See them in SpongeBob SquarePants.
Kesuke Miyagi is a karate expert who thinks the best way a scrawny high schooler can learn how to defend himself is by washing every surface in sight. See them in The Karate Kid.
Combining an innocent face with an insatiable bloodlust, Eli recruits friends to join the vampire way of life. See them in Let the Right One In.
Basil Hallward is dominated, soul, brain, and power by Dorian. See them in Dorian Gray.
A consummate schemer with a knack for solving mysteries, Shawn Spencer has trouble taking anything seriously. See them in Psych.
A life spent as "Number Two" is bound to give Diego Hargreeves an inferiority complex. See them in The Umbrella Academy.