Lord Voldemort

Lord Voldemort (Tom Marvolo Riddle) is the primary antagonist of the Harry Potter series of books. He has appeared in every book except Prisoner of Azkaban.

Name
'I am Lord Voldemort' is an anagram of the name Tom Marvolo Riddle. It is stated that he dropped the name Tom Riddle because it was a legacy of his father, a Muggle, and therefore in Voldemort's eyes inferior to himself.

Most wizards, with two exceptions (Harry Potter himself, and Professor Dumbledore) refuse to say 'Voldemort', preferring to use 'He Who Must Not Be Named' or 'You Know Who' even in print. His followers (The Death Eaters) call him 'The Dark Lord'.

Genealogy
Lord Voldemort is a direct descendant of Salazar Slytherin, and the last of his line, although many Suefics feature his daughter who inevitably attends Hogwarts and becomes friends with Harry and co.

Voldemort's mother was Merope Gaunt, a witch, and his father Tom Riddle Jr, the son of the squire in the village of Little Hangleton. Lord Voldemort had two known relatives on his mother's side: an uncle, Morfin Gaunt, and a grandfather, Marvolo Gaunt. Both died during or after incarceration in the wizard prison Azkaban.

On his father's side both his grandparents were alive, but the teenaged Voldemort killed both, along with the father who abandoned him.

Appearance
Voldemort is described as being 'tall, and skeletally thin' and as having a face 'whiter than a skull, with wide, livid scarlet eyes and a nose that was as flat as a snake's with slits for nostrils'. It is speculated that this inhuman appearance is a result of his surrendering his humanity by creating seven Horcruxes, each containing a piece of his soul.

Actions
J.K. Rowling has described Voldemort as 'a raging psychopath, devoid of the normal human responses to other people's suffering'. During the years he was powerful, he collected a large number of followers who assisted him in carrying out a large number of murders and other acts of terror. Voldemort, in common with many wizards, has a great belief in the 'Purity of Blood'. Those deemed impure, including Muggle-born Wizards, and those with one Muggle parent or grandparent are treated by him as second class citizens. This attitude is not dissimilar to that displayed by Hitler and his Nazis in Germany towards the Jews. J.K. Rowling herself described him as a fusion of the worst aspects of Adolf Hitler and Josef Stalin (both of whom were very bad people.)

Skills
Voldemort is portrayed as being highly intelligent and very powerful. He is an accomplished Legilimens and Parselmouth, and appears to possess the ability to fly unaided by a broom or charm. The core of Voldemort's wand is a tail feather given by the Phoenix belonging to Dumbledore.

In Badfic
''“Ebony.” he yelled. “Thou must kill Vampire Potter! [...] If thou does not, then I shall kill thy beloved Draco!” &mdash;Voldemort, in the infamous My Immortal''

Voldemort in badfic can be anything from an idiot who speaks Fake!Shakespeare (as quoted above) to a loving father who is, presumably, misunderstood. And no, I'm not joking. As Tom Riddle, he is often paired with Hermione or Ginny (via time travel), or even Harry (also usually via time travel). As Voldemort, the same pairings apply, with the additions of Snape, Lucius, and occasionally Bellatrix, Draco, Luna, or Dumbledore. (A tip: Voldemort/Riddle has probably been paired with at least half of the Harry Potter characters at some point. Try not to think too hard about it. In fact, have some bleeopolate.)

Voldemort also gets Sues, usually in the form of a wife, daughter, or granddaughter. A hint: if he's interested in the continuation of his line (ie, in having an 'heir'), he's OOC. If he rapes some woman and then becomes all lovey-dovey with her once their child is born, he's OOC. If he turns out to be rather sensitive, in love with Quirrel, and fond of tap-dancing, then you're dealing with the Very Potter Musical version of him, and you should return him to his home canon/check that you aren't looking at a misfiled AVPM/S/SY fanfic.