D.S. Sally Donovan
First episode: A Study in Pink
Seen also in: The Great Game, The Reichenbach Fall, The Sign of Three
Occupation: Detective sergeant for Scotland Yard
Show history: First seen at a press conference with Lestrade, Donovan is properly introduced as a general pain in the butt in "A Study in Pink" at the crime scene when she calls Sherlock "Freak"; he, in turn, deduces that she is having an affair with Anderson. When Sherlock abandons John, Donovan warns John to stay away from him, as he is a "psychopath."
In "The Great Game," Donovan hands Sherlock the phone when one of Moriarty's "voices" calls and asks for him. Her penultimate contribution to the show occurs in "The Reichenbach Fall," when she is the one who raises suspicions about Sherlock setting up the crimes himself, which leads to his eventual downfall in becoming a fugitive from justice and committing "suicide."
Last seen in "The Sign of Three," she helps Lestrade arrest the Waters crime family.
My take on her: I try not to hate on Donovan too much. Even if she can come across as a bitch, she's really only trying to do her job; Sherlock is the one who keeps intruding on the police's work, even if he does help them solve the crimes in the end. Detective Sergeant is a hard rank to get to, so she obviously is intelligent and has the skills to get to where she is. Add in the fact that there aren't many female Detective Sergeants, and you can see why being routinely insulted by an amateur detective, even if he does happen to be a genius, would make anyone a little irritated. Calling him "Freak" is probably mild compared to what she really wants to call him.
It's really too bad Donovan seems to have served her purpose within the show. Her character existed to bring the show full circle from "A Study in Pink" to "The Reichenbach Fall"; we barely saw her in Season 3 because there's not much left for her to do. She's demonized within the show, a bit unfairly; as I've said before, there's not many people left who will call Sherlock on his crap (minus Molly in "His Last Vow" - those slaps!), so it's sad we seem to be losing one of them.