John Francis Breen, 53, was found unconscious with "serious head injuries" following the incident last night.
He was rushed to hospital but died early today, the Metropolitan Police said.
Officers, who described his injuries as "traumatic", have arrested two 14-year-olds, a 15-year-old and a 16-year-old on suspicion of causing grievous bodily harm.
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Our sympathies go out to Mr Breen's family and I would like to reiterate our appeal for witnesses
Detective Chief Inspector Dave Shipperlee said: "We continue to investigate the circumstances of the incident and are still in the process of interviewing the four teenagers.
"Our sympathies go out to Mr Breen's family and I would like to reiterate our appeal for witnesses to help us piece together exactly what happened."
DCI Shipperlee added: "We have already heard from several people who were at the station, and I would like to thank those who have come forward.
"I am certain there will be more people who cannot only help us with our investigation, but can also provide information that will assist Mr Breen's family in understanding how he sustained such traumatic injuries."
Commuters suffered rush-hour travel disruption at Stratford, close to the Olympic Stadium, after the attack.
Parts of the station were cordoned off by investigating police.
Witnesses at the station said there was "total chaos" after the closure.
Some also described children being trampled on.
However, Transport for London said it had to keep the station open otherwise last night's disorder would have been worse.