Matt Clarke ends Middlesbrough's search for a left-sided centre-back as he joins from Brighton and Hove Albion
The 25-year-old has signed a three-year contract with a further year's option.
Wilder is very particular about how he likes his central defenders to play, and has made a new left-sider a priority this summer.
Since the season started he has been juggling his options there with wing-back Marc Bola and centre-backs Dael Fry and Darryl Lenihan all spending time there within games.
And despite failing to make a single first-team appearances in his three years at Brighton and Hove Albion, Clarke ticks a lot of boxes.
He earned the move to Brighton on the back of an excellent 2018-19 season with League One Portsmouth, and has performed well in two seasons on loan at Derby County and one with West Bromwich Albion.
He has won his club's player of the season award in four out of the last five seasons, and has amassed nearly 300 career appearances by the age of 25.Brighton paid £3m for him in 2019 but Boro's fee is understood to be around £2.25m.
Match fitness could be an issue in the short term, with Clarke yet to feature in a matchday squad this season.