Many emperors were enthusiastic fans of the chariot races. Some also wanted to race publicly, although that was seen as a massively inappropriate thing to do. It should tell you something that Caligula built a private race track (roughly where the Vatican now stands in Rome) because he didn’t want to race openly. He supported the Green faction:
Yet after doing all this he later killed the best and the most famous of these slaves by poisoning. He did the same also with the horses and charioteers of the rival factions; for he was strongly attached to the Greens, which from this colour was called also the Faction of the Leek. Even to‑day the place where he used to practise driving the chariots is called the Gaianum after him. 7 He used to invite one of the horses, which he named Incitatus, to dinner, where he would offer him golden barley and drink his health in wine from golden goblets; he swore by the animal’s life and fortune and even promised to appoint him consul, a promise that he would certainly have carried out if he had lived longer.
Cassius Dio, Roman History 59
Nero (ruled 54-68) was extremely enthusiastic about chariot racing:
Even when Nero was very young he had a deep passion for horses and talked constantly about the games in the Circus, though he was forbidden to do so. Once when he was lamenting with his fellow pupils the fate of a charioteer of the Greens, who was dragged by his horses, and his teacher scolded him, he lied and pretended that he was talking about Hector. When he first became emperor he used to play every day with ivory chariots on a board, and he came from the country to all the games, even the most insignificant, at first secretly and then so openly that no one doubted that he would be in Rome on days when races where held. 2 He made no secret of his wish to have the number of prizes increased, and in consequence more races were added and the performance was continued to a late hour, while the managers of the factions no longer thought it worth while to produce their drivers at all except for a full day’s racing. He soon longed to drive a chariot himself and even to show himself frequently before the public. After a trial exhibition in his gardens before his slaves and the dregs of the people, he gave everyone an opportunity of seeing him in the Circus Maximus, one of his freedmen dropping the napkin from the place usually occupied by the magistrates.
Suetonius, Nero 21
 Originally, an open racetrack, it became a circus and was known as the Circus of Gaius or the Vatican Circus.
 The Greek hero Achilles dragged Hector’s body behind his chariot after he had killed him at Troy. As reading the Iliad, which tells this story, was an important part of Roman education, Nero managed to look like he was talking about school work.