Sunderland have completed the signing of defender Anton Ferdinand from West Ham United on a four-year deal.

Ferdinand, who is thought to have cost the Wearside club £8m, has been drafted in to help reinforce Sunderland's rearguard and has become the Black Cats' ninth signing of the summer.

"We needed to strengthen our defence and Anton is a great signing," said the Sunderland manager Roy Keane. "He's still young but he has over 160 games under his belt so he has experience, he's learning his trade. He'll bring quality and competition for places, which is what we want. Hopefully we can take him to another level here at Sunderland - he has come through the ranks at West Ham and maybe just needs a change."

Ferdinand, who is believed to have rejected a move to Newcastle earlier this summer, admitted that he would find it difficult to leave his hometown club but the England Under-21 international now hopes to improve as a player, much like his elder brother Rio Ferdinand, who left Upton Park for Leeds and subsequently Manchester United. "It was hard leaving West Ham because I have been there for 16 years but after meeting Roy Keane I knew it was time for a change," he said. "This is a great challenge for me and I feel it is an exciting time at Sunderland. I think the move will do me good."

Ferdinand, 23, follows Teemu Tainio, Pascal Chimbonda, Steed Malbranque, Nick Colgan, David Meyler, El-Hadji Diouf, David Healy and Djibril Cissé to the Stadium of Light this summer. And Keane is hoping to reach double figures before the transfer window closes with a left-back thought to be on his radar. "I have one more player in mind and then that is the end of it for a few months at least," he said.