Give me a short summary of the movie Gladiator.
In 180 AD, Hispano-Roman General Maximus Decimus Meridius intends to return home after he leads the Roman army to victory against the Germanic tribes near Vindobona on the Limes Germanicus. Emperor Marcus Aurelius tells Maximus that his own son, Commodus, is unfit to rule and that he wishes Maximus to succeed him, as regent, to help save Rome from corruption and restore the republic. When told of this, Commodus privately murders his father.

Commodus proclaims himself the new emperor, asking Maximus for his loyalty, but he refuses. Maximus is arrested by the Praetorian Guard and is told that he and his family will die. He kills his captors and, wounded, rides for his home near Turgalium (now Trujillo), where he finds his wife and son crucified. Maximus buries them, then collapses from his injuries. Slavers find him, and take him to the city of Zucchabar in the Roman province of Mauretania Caesariensis, where he is sold to gladiator trainer Proximo.

Maximus reluctantly fights in local tournaments, his combat skills helping him win matches and gain popularity. He befriends two other gladiators: Hagen, a German; and Juba, a Numidian. Proximo reveals to Maximus that he was once a gladiator who was freed by Marcus Aurelius, and advises him to "win the crowd" to win his freedom.

When Commodus organises 150 days of games to commemorate his father's death, Proximo takes his gladiators to Rome to fight in the Colosseum. Disguised in a masked helmet, Maximus debuts in the Colosseum as a Carthaginian in a re-enactment of the Battle of Zama. Unexpectedly, he leads his side to victory, and Commodus enters the Colosseum to offer his congratulations. He orders the disguised Maximus, as leader of the gladiators, to reveal his identity; Maximus removes his helmet and declares vengeance. Commodus is compelled by the crowd to let the gladiators live, and his guards are held back from striking them down.

Maximus's next fight is against a legendary undefeated gladiator, Tigris of Gaul. Commodus arranges for several tigers to be set upon Maximus during the duel, but Maximus manages to prevail. Commodus orders Maximus to kill Tigris, but Maximus spares his opponent's life; in response, the crowd chants "Maximus the Merciful", angering Commodus.

Maximus discovers from Cicero, his ex-orderly, that his former legions remain loyal. He meets in secret with Lucilla, Commodus's sister and once the lover of Maximus; and Gracchus, an influential senator. They agree to have Maximus escape Rome to join his legions, topple Commodus by force, and hand power back to the Roman Senate. Commodus learns of the plot when Lucilla's son, Lucius, innocently hints at the conspiracy. Commodus threatens Lucilla and Lucius, and has the Praetorian Guard arrest Gracchus and attack the gladiators' barracks. Proximo and his men, including Hagen, sacrifice themselves to enable Maximus to escape. Maximus is captured at the rendezvous with Cicero, where the latter is killed.

In an effort to win back public approval, Commodus challenges Maximus to a duel in the Colosseum. He stabs Maximus in the lung before the match to gain an advantage. Despite his injuries, Maximus disarms Commodus. After the Praetorian Guard refuses to aid him, Commodus unsheathes a hidden knife; Maximus overpowers Commodus and drives the knife into his throat, killing him. Before Maximus succumbs to his wounds, he asks for political reforms, for his gladiator allies to be freed, and for Senator Gracchus to be reinstated. As he dies, he has a vision where he reunites with his wife and son. His friends and allies honor him as "a soldier of Rome", at Lucilla's behest, and carry his body out of the arena, while the body of Commodus is left behind.

That night, Juba visits the Colosseum and buries figurines of Maximus's wife and son at the spot where he died.