Because you like Frank Costello in The Departed

His murderous megalomania aside, Loki is quite charming. Just don't mention his strapping older brother; he's a tad jealous. See them in Marvel Cinematic Universe.

Severus Snape is a misanthropic potions teacher with a vindictive streak. See them in Harry Potter Series.

A wildly brilliant detective, Sherlock Holmes can figure out everything except how to interact with other human beings. See them in Sherlock.