Former Newcastle defender Jonathan Woodgate has rejoined the club as first-team coach.
Woodgate becomes the latest addition to Steve Agnew's coaching staff following the appointments of Joe Jordan and Paul Jenkins.
"Jonathan is someone who we know very well, and who in turn knows this club inside and out," head coach Agnew told the official Middlesbrough website.
"He brings a wealth of experience from the highest level of the game, and he's a fantastic character.
"We're delighted to have him on board."
Former England centre-back Woodgate represented Leeds, Newcastle, Real Madrid and Tottenham during a distinguished playing career.
He also made 112 appearances for his boyhood favourites Boro in two spells at the club from 2006-08 and 2012-16.
Woodgate announced his retirement shortly after Middlesbrough won promotion to the Premier League in May 2016.
The 37-year-old rejoins the club before their crunch relegation battle against relegation rivals Swansea on Sunday, Agnew's second game in charge since the departure of Aitor Karanka.
Boro are currently five points from safety, but they do have a game in hand on Swansea, who occupy the final spot above the relegation zone.