Former West Ham boss Sam Allardyce takes over at Sunderland
Dick Advocaat quit Sunderland on Sunday with the Black Cats second-bottom of the Premier League and winless in their opening eight games.
Allardyce, 60, has been out of management since he left West Ham at the end of last season.
"Of course it's a challenging job. But I hope to be able to help to bring the stability and success that everyone wants," Allardyce said.
"I'm looking forward to working with the players and of course I will be relying on the help of the Sunderland supporters."
Allardyce had a spell at Sunderland as a player between 1980 and 1981 and becomes the first person to manage both the Black Cats and rivals Newcastle.
His first home game at the Stadium of Light will be against Newcastle on 25 October, with an away trip to West Brom before that on 17 October.
Sunderland owner Ellis Short believes Allardyce, who managed Newcastle from May 2007 until January 2008, was the standout candidate for the job.
"Sunderland is a club he knows well and he was the obvious best choice for the job," Short said.
"He has vast experience of managing in the Premier League and an understanding first-hand of the north-east and the passion of our fans, which will stand him in great stead."
Allardyce is the first manager to look after both Newcastle and Sunderland. Rumours in Essex suggest Southend boss Phil Brown might re-join Allardyce. They had a hugely successful spell together at Bolton. Allardyce could also turn to his other former assistant, Neil McDonald who is currently boss of cash strapped Blackpool. McDonald took over the Lancashire club when he left West Ham with Allardyce in the summer.