Dobby

Appearance
Dobby has huge, green, tennis ball-sized eyes and a long thin nose like a pencil (CS1, CS2). He is quite short, like all house-elves, coming only up to Harry's navel (GF21).

Clothing during slavery: an old pillowcase, with rips for arm- and leg-holes.
Clothing after independence: "a tea cozy for a hat, on which he had pinned a number of bright badges; a tie patterned with horseshoes over a bare chest, a pair of what looked like children's soccer shorts, and odd socks.  One [...] was the black one Harry had removed from his own foot [...] The other was covered in pink and orange stripes." (GF11). Later that year Ron gives him a maroon sweater that his mom made (GF23), and in Book 5, Dobby began wearing all the hats (2-3 ft. high), scarves and socks that Hermione knitted for the house-elves (OP18) because the others found Hermione's attempts to free them "insulting."

Socks: Socks, of course, are extremely important to Dobby, symbolizing empowerment and freedom, the rewards for his service to Harry. It is no wonder that in Book 4, Dobby begins knitting socks with wool purchased with his wages. For Christmas that year he made Harry a mis-matched pair:  the left sock was bright red and had a pattern of broomsticks upon it; the right sock was green with a pattern of Snitches. Throughout the books, Dobby wears or owns

• the black "slimy" one Harry gave him (GF11),
• a mustard yellow pair from Harry (GF23),
• a violet pair from Ron (GF23),
• lurid socks purchased by Harry in Hogsmeade, including a pair patterned with flashing gold and silver stars, and another that screamed loudly when they became too smelly (GF27),
• socks Hermione made and left for the Hogwarts house elves (OP18).

LANGUAGE
Dobby speaks about himself in the third person ("Dobby will have to punish himself most grievously for coming to see you, sir.") and tends to get his verb tenses mixed up ("I has seven now, sir"). Dobby refers to Ron as Harry's "Wheezy." (GF)

SKILLS
JKR has told us that House-elves have their own kind of magic (JKR). In addition to knitting socks and painting, Dobby has performed some rather powerful charms -- apparently without the need for a wand:

• He enchanted a Bludger,
• closed the magic portal that leads to platform 9 ¾,
• interfered with Owl Post and stole letters, and
• knocked Lucius Malfoy down a flight of stairs.
• He also can disappear at will, even at Hogwarts where Apparition is "simply not possible."
• Dobby claims to be a secret keeper for Dumbledore.
• Apparated in and out of an "escape proof" cellar at the Malfoy mansion.

Is Dobby a help or a hindrance?
Note that as long as Dobby was the slave of the Malfoys, his attempts to help Harry failed:

• the stolen Owl Post (CS1),
• the closed magic portal leading to Platform 9 ¾ (CS2),
• the enchanted Bludger (CS5, CS10).

But after Harry Potter freed Dobby from the Malfoys, Dobby

• knocked Lucius Malfoy down a flight of stairs (CS18),
• gave Harry Gillyweed so he could breathe underwater and rescue Ron (GF26),
• he explained how and where Harry could find the Room of Requirement (OP18),
• and warned the members of the DA when Umbridge discovered their secret (OP27),
• tailed Draco (HBP19, 21),
• Apparated into the Malfoy Mansion on a rescue mission from Aberforth (DH23),
• Rescued Luna, Dean Thomas and Ollivander from an "escape-proof" cellar (DH23),
• Dropped a chandelier on Bellatrix (DH23),
• Stripped Narcissa of her wand (DH23),
• Rescued Griphook, Harry, Ron, and Hermione from certain death (DH23).