One of the Weasley family's owls, Errol was ancient by the time we meet him in the books. Errol was somewhat unreliable due to his poor eyesight, which caused him to hit objects in mid-flight.
Harry Potter and the Philosopher's Stone
Harry Potter and the Chamber of Secrets
Harry Potter and the Prisoner of Azkaban
Harry Potter and the Goblet of Fire
The Weasleys
Delivering post... sometimes
Flying head-first into windows