Mark Antony was perfectly willing to serve as Caesar's subordinate. He had no ambition to surpass him but would have been loyal to him indefinitely if he had not been killed. That is one reason why Antony does not seem as ambitious as Julius Caesar.
When Antony had the whole Roman citizenry in the palm of his hand after the success of his funeral oration, he did not consider seizing sole power, as he could have done. He formed a triumvirate with Julius Caesar's heir Octavius and even included Lepidus in the ruling trio, although he did not respect him. Antony does not seem like a shrewd, calculating, unscrupulous type of man. He is spontaneous, fun-loving, reckless--not like either Caesar or Octavius. Octavius ends up being the sole ruler of the Roman Empire. Antony was quite content to be ruler of the eastern half of that empire. He didn't have big ambitions or big plans. He lived from day to day. He was not a deep thinker. He spent a lot of his time in bed with Cleopatra or partying. He simply did not take life seriously--as did Julius Caesar, Octavius, Brutus, and Cassius: to Antony life was a game. That is what we like about him.
Antony was a better man than Julius or Octavius in some respects. He was unselfish and generous. In Antony and Cleopatra, Cleopatra describes him in terms that are somewhat extreme but not totally inaccurate.
His legs bestrid the ocean; his rear'd arm
Crested the world: his voice was propertied
As all the tuned spheres, and that to friends;
But when he meant to quail and shake the orb,
He was as rattling thunder. For his bounty,
There was no winter in't; an autumn 'twas
That grew the more by reaping: his delights
Were dolphin-like; they show'd his back above
The element they liv'd in: in his livery
Walk'd crowns and crownets; realms and islands were
As plates dropp'd from his pocket.
Think you there was or might be such a man
As this I dream'd of?
Gentle madam, no.
Octavius could not have become emperor if Antony had not helped him by turning the mob against Brutus and Cassius with his funeral oration and also helped Octavius, an inexperienced warrior, win the battle of Philippi. If Antony had not helped Octavius, then Octavius never would have been there to defeat him years later. Antony had the only copy of Caesar's will. If he had been ambitious he could have thrown the document in the fire and seized sole power in Rome. Antony was highly regarded by Caesar's army because he was a good leader, a brave soldier, and a generous man; it would have been easy to take control of the army and seize all the money he needed to pay the soldiers. He would have had to fight Brutus and Cassius, but he was just as capable of doing so without Octavius as he was with him.
In Shakespeare's Twelfth Night, Malvolio writes in a letter:
some are born great, some
achieve greatness, and some have greatness thrust upon 'em.
Act 2, Scene 5
Julius Caesar was born great. Octavius Caesar achieved greatness. Mark Antony seems to have been one of those men who have had greatness thrust upon them.