The England under-21 centre-half signed a four-year deal, becoming 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.

"I don't think (Alan) Curbishley is controlling who is going out the door. The finances are dictating things, and the board are making all the decisions

"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."

Keane revealed he is keen to make one more signing before the transfer window closes on Sunday night.

He said: "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 have to wait until September 13 against Wigan to make his Black Cats debut.