Bilius

Bilius (surname either Prewett or Weasley) was a pure-blood wizard and a brother of either Arthur Weasley or Molly Weasley. A lifelong bachelor, he was fun-loving and lively, but was prone to eccentric behaviour. He reportedly died twenty-four hours after seeing a Grim.

Biography
Bilius was a brother of either Arthur Weasley or Molly Weasley née Prewett and an uncle to the couple's seven children, as well as the namesake for the youngest son, Ronald Bilius Weasley.

Bilius never married and presumably had no children. According to his nephews, Fred and George Weasley, he was always a joker, and was fun to have at weddings and parties. On more than one occasion, he was said to have consumed an entire bottle of Firewhiskey and then run to the dance floor, where he lifted his robes and began to pull bouquets of flowers out of an alarming part of his body.

Bilius was said to have gone "loopy" towards the end of his life. According to his nephew Ron, he died twenty-four hours after having seen a Grim sometime in or prior to September 1993.

Etymology
"Bilious" is the adjective for 'bile,' a yellowish-green secretion of the liver. The word "bilious" goes back to the old belief that there were four bodily humours (black bile, yellow bile, phlegm, and blood) and these four humours determined a person's temperament. "Bilious" was the personality type associated with an excess of yellow bile, and indicates a peevish, ill-natured disposition.

Behind the scenes

 * It is often presumed that Bilius was Arthur Weasley's brother, as J. K. Rowling revealed that Arthur was "one of three brothers," but did not give the names of the other two brothers. However, it is still possible that Bilius was a brother of Molly Weasley née Prewett, as although Rowling has confirmed that Fabian and Gideon Prewett were Molly's brothers, she has not stated that they were Molly's only brothers.
 * Bilius seemed prone outrageous behaviour, and is hinted to be an alcoholic.
 * If Bilius was the brother of Molly, then he would distantly link to the House of Black, for Molly's aunt by marriage is Lucretia Prewett nee Black. If he was the brother of Arthur, it would be the same: Arthur's mother was Cedrella Weasley nee Black.

Appearances

 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Deathly Hallows

Notes and references
Bilius