Ferdinand is a graduate of the West Ham youth system
Sunderland have completed the signing of defender Anton Ferdinand from West Ham for a fee of about £8m.
The England under-21 centre-half has signed a four-year deal at the Stadium of Light, and becomes manager Roy Keane's ninth signing of the summer.
"We needed to strengthen our defence and Anton is a great signing," said Keane. "He'll bring in quality and competition for places, which we need."
Ferdinand, 23, added: "After meeting Roy I knew it was time for a change."
The signing follows those of Teemu Tainio, Steed Malbranque, Pascal Chimbonda, Nick Colgan, David Meyler, El-Hadji Diouf, David Healy and Djibril Cisse this summer.
"It was hard leaving West Ham because I have been there for 16 years," said Ferdinand.
"But this is great challenge for me and I feel it is an exciting time at Sunderland. I think the move will do me good."
Ferdinand will be in direct competition with Nyron Nosworthy, Danny Collins and Danny Higginbotham for a place in the centre of defence.
It is a position that Keane has been looking to strengthen over the summer, with Jonny Evans having returned to Manchester United after his loan ended.
And Keane also revealed that he is keen to make one more signing, saying: "I have one more player in mind and then that is the end of it for a few months at least.
"I will be delighted if I can get him and then we can concentrate on the season."
Ferdinand, the younger brother of Manchester United star Rio, is recovering from a hamstring strain and will therefore have to wait until the Wigan game on 13 September to make his Black Cats debut.