The Quibbler

The Quibbler is a fictional magazine of the Harry Potter world. 
"The Quibbler" is written by Xenophilius Lovegood, father of Luna Lovegood. The magazine is meant to cause shock, and contains the strange opinions of Xenophilius. Luna believes in everything her father says and during the "Order of the Phoenix" she had lots of arguments with Hermione Granger about it.
"The Quibbler" often has articles about creatures that other characters believe to not exist. In "Harry Potter and the Order of the Phoenix", it published an interview between Rita Skeeter and Harry Potter. In this interview, Harry said that he had seen Lord Voldemort.
For most of "Harry Potter and the Deathly Hallows", "The Quibbler" writes positive views on Harry, and tells people to support him. However, after Luna is taken by the "Death Eaters" (supporters of Voldemort), Xenophilius turns against Harry and begins posting wanted signs for him in "The Quibbler". When Harry visits him for information on the "Deathly Hallows", Xenophilius turns him in to the Death Eaters. Harry narrowly escapes.