As players they never gave less than 100 per cent on the pitch.
Now two legends of Manchester United and Liverpool - Roy Keane and Graeme Souness - will be battling to make themselves heard on the Sky Sports panel when the North West rivals meet on Sunday.
It's a game the home side will be confident of winning given their form this season and the incentive of putting even more points between them and Jose Mourinho's side will make for an electric atmosphere.
Keane is well known for his blunt style of punditry and is not afraid to pull any punches. He has been highly critical of United this season - especially Mourinho - while Souness is similarily unbothered by reputations. His views on Paul Pogba's performances have been well documented - falling out with the likes of Jamie Redknapp and Gary Neville over the French World Cup winner.
The game kicks off at 4pm but Keane and Souness will also be in the studio for the lunchtime game between Southampton and Arsenal.
As a player, Keane played in 21 games between the two teams, winning nine, losing seven. TV viewers will be praying for some juicy anecdotes from one of the biggest games in the football calendar.
Jamie Carragher will also be on the panel at Anfield with Gary Neville on duty as co-commentator. Liverpool boss Jurgen Klopp will be hoping for the kind of atmosphere which inspired his team to a Champions League win over Napoli on Tuesday.
