"Lockhart'll sign anything if it stands still long enough."
-- Ron Weasley (CS10)
Lockhart was born to a Muggle father and witch mother. The latter thought of him as her favourite, which undoubtedly led to his inflated sense of self-importance. When he began attending Hogwarts on 1st September 1975, where he was sorted into Ravenclaw house, he came to the sudden realisation that he was not as exceptional as he had previously thought. Despite being of above-average intelligence, he became lazy with his school work, more interested in being the centre of attention (Pm).
After school, Lockhart travelled the world, writing books about his exploits fighting various types of magical creatures, but the truth is that he simply interviewed the folks who really dealt with the creatures, then performed Memory Charms on them. For over a decade his fakery was undetected, and he received numerous awards including the Order of Merlin 3rd Class, honorary membership of the Dark Force Defence League, and Witch Weekly's Most-Charming-Smile Award.
Albus Dumbledore, who knew two of the people who had been victims of Lockhart's Memory Charms, hired him in order to expose him as a fraud, tempting him back to the school with the promise of being Harry Potter's Defence Against the Dark Arts teacher (Pm). Throughout the academic year, Lockhart proved himself to be inept in almost all aspects of magic.
In June of 1993, while in the Chamber of Secrets, Lockhart accidentally blasted himself with the Memory Charm he was aiming at Ron and Harry. He lost his memory entirely as a result.
Lockhart is currently a resident of the Janus Thickey ward (a closed, longterm ward for patients with permanent spell damage) at St. Mungo's Hospital, where he tends to wander off and get lost (OP23). Hospital ward-mates include Agnes (a fur-faced woman), Broderick Bode (now deceased), and Alice and Frank Longbottom, Neville's parents. He has recently mastered "joined-up" (cursive) writing. He gets fan mail all the time, although he has no idea why.
Lockhart wrote a promotional blurb for Quidditch Through the Ages (QA).
Mother: a witch, who considered Gilderoy her favourite child.
Father: a Muggle.
Siblings: two older sisters, both Squibs.
Lockhart perfected the Memory Charm, which he used to take credit for the exploits of other, more talented, witches and wizards.
Gilderoy: The name of a handome highwayman in the Dictionary of Phrase and Fable.
Lockhart: A traditional Scottish surname which JKR found on a war memorial.
Lockhart is the only character in the series to date to use a peacock-feather quill. The peacock is a traditional symbol of vanity, a very apt implication in Lockhart's case. His large, colourful wardrobe would also qualify him to be referred to as a "peacock" in the slang sense. (Peacocks also have other, more positive symbolism associated with them, but this is the most common modern English usage.) - MLW