Dr Mullen had already captained Ireland to their first-ever Grand Slam, two Triple Crowns and two International Championship titles when he was selected as the man to lead the Lions against the Wallabies and All Blacks on the first Lions adventure since the 1938 tour of South Africa.
The popularity of the 1950 tourists, who are still talked about in glowing terms by the New Zealand and Australian public, owes a great deal to the affable nature and tactical astuteness of Mullen himself.
Arguably the most-talented hooker of his generation, Mullen recognised the strengths of a superb Lions backline and did his best to ensure they were given the necessary possession to show off their undoubted skills.
He knew when to change tact during a game and coached the Lions forwards throughout the tour in an era in which the Lions were required to coach themselves.
Dr Mullen won a total of 25 caps for his country between 1947 and 1952 and went on lead Ireland to another International Championship crown a year after returning home with the Lions.
Dr Mullen's Ireland and Lions team-mate Jack Kyle echoed the thoughts of many of those who played with and against him when he gave this assessment of his international captain.
"Karl was very unassuming, and certainly did not push his weight around when he was captain.
"He was quietly authoritative and a superb technical player. Karl didn't say much as captain but when he did it was straight to the point.
"He led the Lions to New Zealand and Australia, and it was a very successful tour considering that we were away for six months. We did well in Australia and sang our way through New Zealand!
"Karl was only 22 when he was made captain of the Ireland side in that memorable 1948 season.
"Before the final game at Ravenhill he just said 'We have a job to do here today, so let's get on with it'.
"He had a very happy life and it is sad that he has passed away."