The man who was in charge of policing on the day of the Hillsborough disaster will today give evidence to inquests into the deaths of 96 football fans.
David Duckenfield was match commander on 15 April, 1989, and has been heavily criticised for blaming Liverpool supporters for creating the incident.
The inquests have already heard that Mr Duckenfield, a former chief superintendent, gave the order to open an exterior gate to ease congestion at the Leppings Lane end outside the Sheffield stadium, but is alleged to have told officials that Liverpool fans had forced it open.
For many relatives of those who died in the disaster Mr Duckenfield is the most important figure from South Yorkshire Police to give evidence.
At the opening of the hearings last year the coroner, Lord Justice Goldring, told the jury that Mr Duckenfield was in overall control of "F" Division, where the Hillsborough stadium is based.
The police officer had been promoted just weeks earlier and had never been in charge of a match at Hillsborough before the FA Cup semi-final between Liverpool and Nottingham Forest.
Lord Goldring told the jury: "Whether that was a sensible decision may be something for you to have to consider."
Members of the jury have been told that the then chief executive of the Football Association, Graham Kelly, went to the police control box after the match had been stopped and spoke to Mr Duckenfield.
Mr Kelly told an earlier hearing: "I said 'what has happened?' and Mr Duckenfield said 'the Liverpool fans have forced a gate'."
The officer in charge of the Leppings Lane turnstiles, Superintendent Roger Marshall, has already told the inquests that was a lie.
Michael Goddard, a former police sergeant who shared the control box with the match commander, told the inquests that Mr Duckenfield "did not step up to the plate" as the disaster unfolded and had made a "gross error" in failing to consider the effect of opening an exterior gate.
Although Mr Duckenfield was in charge of policing the Hillsborough match he was not the most senior South Yorkshire Police officer at the stadium. Assistant Chief Constable Walter Jackson was the senior officer on call for the day.
Asked during his evidence whether it had been right for Chief Supt Duckenfield to take control of the semi-final he said: "He had reached a senior rank in the service and you don't get to be a deputy divisional commander if you haven't got tremendous experience."
Mr Duckenfield is due to give evidence at the inquests for four days.