Sunderland have completed a deal for four players to join the Stadium of Light.
Midfielder Sebastien Larsson and goalkeeper Keiren Westwood officially join on free transfers following their release from Birmingham City and Coventry City.
Ji Dong-won joins English football from Chunnam Dragons, while Craig Gardener is the Black Cats' second recruit from Birmingham.
Gardner said: "It's unbelievable, to be honest.
"As soon as it came out that Sunderland were interested in me it was a no-brainer.
"I've heard so much about Steve Bruce, his backroom staff and how good a chairman Niall Quinn is.
"Sunderland are a massive club and their ambitions match mine. It was too good a move to turn down."
Ji joins the likes of Ji-Sung Park and Chung-Yong Lee in the Premier League and the Korean is proud to be representing his country in what he calls the world's biggest league.
"I am so satisfied to be able to come to a good club, a nice club, in the world's number one league," he said.
"I am happy because I have a chance to challenge the biggest players, and that gives me motivation."
The four-some join Connor Wickham, who joined Sunderland from Ipswich Town for £8 million, on Wednesday.