He is the proprietor of the Corrida Colosseum of Dressrosa, where he earned his title as the "Hero of the Colosseum".
Diamante wears a light colored hat with brown locks of hair coming down from it. He has striped, orange and red rectangular streaks that run down from his forehead, through his eyes, straight to his chin. In the digitally colored manga, he wears a pink shirt with purple pants and a crimson cape made of steel, while in the anime, Diamante dons a light colored shirt with brighter red pants that match his cape. He is an extremely tall and thin man, at least a foot taller than Doflamingo who is 10 feet tall himself, and possesses a muscular upper body. His legs are especially long, protruding out right next to his face when he sits down. Of the top three officers of the crew, he is the lankiest and thinnest.
Ten years ago during the takeover of Dressrosa, the streaks on his face were not present.
Every time someone says something flattering or good about Diamante, he denies it until the person flattering him stops. That is when he accepts the compliment, and believes that the person praising him had offered his or her unbiased opinion about his talents.
He is also very cruel, as he spoke to Bellamy extremely harshly after he was beaten in the Colosseum. During the usurpation of the Riku Family, he was seen smiling during the burning down of the castle, indicating his joy during the event. This attitude extends to all new recruits, even children, as he shows them little respect. Diamante also is rather insensitive and monstrous and he was bluntly telling Rebecca about her mother's death on top of mocking her father for his sorrow over her loss; he also called Corazon lacking in intelligence and concentration right in his face. Despite this, he has no tolerance for anyone who mocks his crew, whom he sees as family members, being visibly infuriated and stunned when a foot soldier laughed at Pica's high pitch voice.
Diamante does not seem to give in to popular opinion as he remained steadfast in declaring Rebecca the winner of block D when some other gladiators tried to attack her, showing at least fair sportsmanship. He also believes one must be honest with money, telling Corazon to hand over the earnings from his job.
Like many One Piece characters, Diamante has a distinct laugh: "Uhahahaha".
As the director of the Corrida Colosseum, he is in charge of all the goings on in the building. He is also known as the "Hero of the Colosseum" on Dressrosa, for which Doflamingo holds him in high regard. In addition, he sits in Doflamingo's diamond chair, one of the four executive officers of the crew.
Doflamingo trusts Diamante enough to fight all of the block winners in the tournament alone, as the Battle Brigade that he commands has been sent away to complete various tasks. This implies that Doflamingo has enough confidence in Diamante's strength and abilities to at least compete against, if not defeat, Jesus Burgess, Bartolomeo, Rebecca, and Lucy by himself. He is also somewhat durable, as he was not bothered by Rebecca striking him in the leg with her blunt sword.
Diamante was able to defeat the entire Dressrosa army, alongside Trebol and Pica.
He is able to recognize Haki, as he noted the clash between Luffy's Haki and Don Chinjao's.