RMT union leader Bob Crow passed away in the early hours of the morning, aged 52, the union has confirmed with 'deepest regret'.
The general secretary of the Rail Maritime and Transport (RMT) union suffered an aneuyrsm and heart attack at Whipps Cross Hospital in Leytonstone.
Crow was a controversial figure, identified by many with tube strikes which crippled London’s transport infrastructure.
London Mayor Boris Johnson, who clashed with Crow on his plans for the Tube said in a statement: 'I am shocked. Bob Crow was a fighter and a man of character.
He added: 'Whatever our political differences, and there were many, this is tragic news. Bob fought tirelessly for his beliefs and for his members.
'There can be absolutely no doubt that he played a big part in the success of the Tube, and he shared my goal to make transport in London an even greater success.'
Former London mayor Ken Livingstone told ITV: ‘His [Crow] members are one of the few groups of working class people who have still got well paid jobs and a lot of that is down to him.’