Dobby
Age: Unknown
House: N/A
Distinguishing Characteristics: Dobby is a house-elf. He is short with big bat-like ears, bulging green eyes the size of tennis balls, and a long, thin nose. In the old days, when he was a servant of the Malfoy family, he wore nothing but an old pillowcase. Following his emancipation, he wears as much as he can fit on his body. Dobby has a penchant for beating himself up.
Heritage: Elf
Family: Unknown, though it is likely that his ancestors worked for the Malfoy family as well.
First Mention: Chapter one of Chamber of Secrets
General: Dobby was the downtrodden servant of the Malfoy family for many years, where he was subjected to frequent threats, humiliation, and abuse (which is often the lot of the house-elf). Most house-elves seem to accept this as standard practice and do not seek to change it. Dobby, however, disliked his masters and sought to help Harry when he heard that they were plotting against him.
This is where the self-abuse comes in; Dobby was breaking his orders and hence had to punish himself. His commitment to Harry's cause (and his hatred for the Malfoys) was enough to make him willing to do this, though, even if it meant ironing his hands. Harry (with some helpful advice from Dobby along the way) managed to thwart Lucius Malfoy's plan and even managed to trick him into giving Dobby a sock. The act of giving clothes releases a house-elf from servitude; ergo, Dobby was free.
After enjoying his freedom for a while, Dobby went to work with the large house-elf contingent at Hogwarts, where he is regarded somewhat suspiciously by his peers--firstly for his lack of a submissive attitude, and secondly for the fact that he actually gets paid a nominal amount for his labours. Both of these are seen as scandalous by other house-elves, who want nothing more than to serve.
Dobby collects clothes and even attempts to knit them himself, and has maintained his friendship with Harry wherever possible. Knowing the behind-the-scenes routes at Hogwarts as he does (as a house-elf should never be seen), he has proved to be extremely useful.
Due to his knowledge of Hogwarts' layout, he was recently and reluctantly teamed up with Kreacher (whom Harry inherited from Sirius) to follow Draco Malfoy around the school when Harry became suspicious of his actions. Neither Dobby nor Kreacher was happy about this arrangement, and at one point their warring loyalties came to blows. However, they were able to provide Harry with vital information that helped him begin to understand how to "catch" Draco. As always, Dobby remains highly loyal to Harry Potter, and has already cemented his place time and time again as a friend and useful ally. In the ensuing war, Harry would do well to remember that.