OJ Simpson's trial is expected to last around five weeks
The robbery trial of the former US football star, OJ Simpson, has opened in Las Vegas with prosecutors urging the jury to unmask his "true face".
Mr Simpson is accused of robbing two sports memorabilia dealers a year ago.
He faces 12 charges including kidnap, armed robbery and assault with a deadly weapon. If found guilty of kidnapping, he could receive a life sentence.
Mr Simpson, 61, who denies the charges, was acquitted of murder in 1995 in what was dubbed "the trial of the century".
He had been accused of murdering his former wife Nicole Brown Simpson and her friend Ronald Goldman in 1994. The not-guilty verdict shocked many in America.
Mr Simpson was later found liable for the deaths in a civil case and ordered to pay $33.5m to the victim's families.
The sporting icon has remained a polarising figure in American popular culture ever since, correspondents say.
OJ Simpson smiled and gave a thumbs-up sign to a handful of onlookers as he arrived at court on Monday.
The charges against him and his co-defendant Clarence Stewart, 54, stem from a confrontation with two collectibles dealers in a Las Vegas hotel last September.
Mr Simpson is accused of storming the room with five other men - some of whom were armed - and leaving with hundreds of items largely relating to Mr Simpson's sporting career. The dealers say the items were theirs to sell.
In his opening statement, Chief Deputy District Attorney Chris Owens said Mr Simpson showed "a pattern of arrogance coupled with hypocrisy" and urged jurors to unmask his "true face."
Mr Owens then played an expletive-filled audio recording of the hotel room incident.
"The audio will show threats, it will show force, it will show demands and it will show the taking of property from the victims in this case," he told the court.
Opening the case for the defence, Yale Galanter asserted that the evidence would not show Mr Simpson had intended to commit a crime, but rather that he went to the hotel to retrieve personal property that had been stolen from him by "hustlers".
"This was a recovery; this wasn't a robbery," he said.
Mr Galanter also said that the audio played by the prosecution also showed his client telling people who had stormed the room with him: "Don't take any things that aren't mine."
The trial was later interrupted when one of the key witnesses for the prosecution received medical attention from paramedics after apparently complaining of chest pains.
Bruce Fromong, one of the two sports dealers who claims to have been robbed by Mr Simpson, was treated for dizziness and overheating after clutching his chest in the courtroom.
During questioning by defence lawyers, he appeared to weep as he described how the alleged actions of Mr Simpson, whom he had once regarded as a friend, had hurt his feelings.
The trial is expected to last five weeks. Four of the gang have struck plea deals in exchange for testifying against Mr Simpson.