Because you like Jim Moriarty in Sherlock
Khan Noonien Singh is super strong, super smart, and out for revenge. He always seems to be two steps ahead of his enemies. See them in Star Trek Into Darkness.
This power-hungry Time Lord calls himself the "master of all." Bonus: he has 13 lives. See them in Doctor Who.
Jenny Flint is a devoted wife and daring crime fighter, which is pretty unconventional for a Victorian maid. See them in Doctor Who.
Fiery and adventurous, Amy Pond is the sort of woman you'd want by your side on a journey through time and space. See them in Doctor Who.
Javert is an inspector with a single-minded focus: to bring criminals to justice. See them in Les Miserables.
James Gordon happens to be the one guy in Gotham City with proper morals who doesn't also run around in a cape. See them in DC Extended Universe.
Gilderoy Lockhart's biggest idol is himself. See them in Harry Potter Series.
A suave demon, Crowley grants humans their wishes in exchange for their soul, only to find loopholes that benefit him. See them in Supernatural.
Point the fun-loving Pippin Took towards second breakfast, and he's one happy hobbit. See them in The Lord of the Rings.
Rory Williams is a caring companion whose specialty is looking after others. See them in Doctor Who.
Manipulative, conniving, and ruthless, Mr. Gold is enigmatic no matter what world he's in. See them in Once Upon a Time.
Donna is boisterous and spunky traveller of the TARDIS, exploring worlds beyond the simple mundane enterprises of Earth. See them in Doctor Who.