Nicholas Winton was a young, left-leaning stockbroker in 1938, when a friend cancelled their planned skiing holiday in Switzerland and invited him to Prague instead.
He found himself visiting camps for refugees from the Sudetenland, an area under Nazi occupation.
British activists were already in Czechoslovakia trying to help them, but Mr Winton's brainwave was to rescue the children by finding families in the UK to give them a home.
Being from a German Jewish family - his mother's family were all in Germany at the time - he was well aware that Hitler was dangerous and that the situation was urgent.
On his return to London he started looking for families to host the Czech children, and got the Home Office to agree to let them in.
His collaborator in Prague, Trevor Chadwick, compiled a list of thousands of children keen to leave.
"The problem was getting the people who would accept the children, and of course this was at a time when the evacuation of children from the south [of England] was taking place anyway..." he says.
"It's marvellous that so many people did come forward. The unfortunate thing was that no other country would come along and help. I tried America but they didn't take any. It would have made a vast difference if they had."
Mr Winton didn't return to Prague during the six months that the trains were operating.
He continued working on the stock exchange during the day, and running the London end of his Czech operation from 4pm into the evening.
Altogether, 669 children were rescued in eight separate trains.
Nicholas Winton was born in May 1909, and baptised a Christian. He does not subscribe to any faith.
He was knighted in 2003.