Ernest Mangnall, from Bolton is still the only man to have ever managed both Manchester United and Manchester City, though he began his managerial career at Burnley in 1899 (aged 33).
His managerial career began with relegation with Burnley in his first season, but soon led to Manchester United, where he became the first ever manager of Manchester United. He was hired as the club came out of the bankrupcy which had led Newton Heath to fold and re-emerge as Manchester United. He was also the club's first successful manager as he led the club to their first ever League title, beating Aston Villa by 9 points. He then followed that up with the club's first FA Cup (beating Bristol City 1-0). He then won the title for the second time in 1911 - again beating Aston Villa into second place, but this time by only one point. This was to be the club's last title for 40 years - the longest run without the title.
A season later, he left the club and made what today would be an impossible trip - across the city to Maine Road, taking over the blue half of the City. He stayed there for 12 years (second only in terms of service to Wilf Wild). Although no silverware came his way during his time with Manchester City, he steadied the the club and gave it strong foundations for the growth of football in this country.