Under O'Neill's tutelage, Lennon excelled at Celtic and went on to collect five championship winners' medals, three Scottish Cups and two League Cups.

BBC: Lennon takes Celtic centre stage

He led Aberdeen to three Scottish titles, four Scottish cups, one League Cup and one European Cup Winners' Cup before moving to Manchester United in November 1986 following the dismissal of former manager Ron Atkinson.

CNN: Alex Ferguson retires as Manchester United manager

He has a tough act to follow, as in four seasons under Gordon Strachan Celtic celebrated three SPL titles, a Scottish Cup, two League Cups and two appearances in the Champions League last 16.

BBC: Mowbray the natural leader