Doctor Quackenhoof, the worst doctor in Equestria.
Doctor Grizelda J. Quackenhoof (the J. is for "Edgar") is a pink Earth Pony who bears a remarkable resemblance to Pinkie Pie, except with bushy eyebrows, a moustache (which she claims is not hers, she's "holding it for a friend"), a giant fake nose and glasses. She often smokes cigars.
Very little of her background is known, and what little is known, is frankly unreliable. She often claims to have treated anypony and everypony from Princess Celestia to Granny Smith. She also frequently mentions her husband, who at various times is said to have left her, to be missing, or to have died. She is occasionally flirty, especially with colts, but is just as likely to turn around and insult them.
It's not entirely clear what Dr. Quackenhoof's skills are; she frequently talks about what a terrible doctor she is, so presumably medicine isn't one of them. She does have a quick wit and a seemingly-endless supply of terrible jokes. She is constantly broke and trying to come up with ways to make a quick bit, often referring to being homeless, hungry, or generally down on her luck. On the other hand, when she does come into large sums of cash, she's prone to turning around and handing it to the first pony in need she sees.