The RMT has confirmed reports that Bob Crow has died at the age of just 52.
In a statement on its website, it said: "It is with the deepest regret that RMT has to confirm that our General Secretary Bob Crow sadly passed away in the early hours of this morning.
I’m shocked. Bob Crow was a fighter and a man of character.
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.
It’s a sad day.
I assumed he would be at my funeral not me at his.
He fought really hard for his members. The only working-class people who still have well-paid jobs in London are his members.”
With the passage of time people will come to see that people like Bob Crow did a very good job.
Bob Crow was a major figure in the labour movement and was loved and deeply respected by his members.
I didn’t always agree with him politically but I always respected his tireless commitment to fighting for the men and women in his union. He did what he was elected to do, was not afraid of controversy and was always out supporting his members across the country.
He was a passionate defender of and campaigner for safe, affordable public transport and was a lifelong anti-fascist activist.
My thoughts are with his family, friends and colleagues in the RMT and wider union movement at this difficult time.
This is shocking news. Bob was an outstanding trade unionist, who tirelessly fought for his members, his industry and the wider trade union movement.
He was always a good friend and comrade to me. We will miss him, and our thoughts are with his family and the RMT at this difficult time.
Manuel Cortes, TSSA rail union leader
Bob Crow was admired by his members and feared by employers, which is exactly how he liked it.
It was a privilege to campaign and fight alongside him because he never gave an inch.
Paul Kenny, GMB general secretary
The loss for members of the RMT is immeasurable. They have lost their champion. The loss to the trade union movement and to the cause of advancing the living standards of working people across the globe is devastating.
Even people who didn’t like what he did agreed he did it very well. Our thoughts are with Bob’s family and the RMT.
Bob’s strength, personal integrity and straight forward speaking won many battles for his members. He took his job very seriously and never stopped working. A giant of the labour movement. He is irreplaceable.