Diamante (ディアマンテ Diamante) is an elite executive and leader of Donquixote Pirates' Diamante Army. He's one of the major antagonists in the Dressrosa Arc. He was the one who was responsible for the death of Rebecca's mother, Scarlet.
Diamante is a rather laid back man who likes to get praised for his achievements and power. While he enjoys the attention, he usually likes to deny it to some extent like in some of his conversations with Donquixote Doflamingo. Diamante is also very arrogant and thinks that he can obtain the Mera Mera no Mi in his battle against Rebecca, Jesus Burgess, and Lucy. He is shown to be down right sadistic as he mocks Rebecca for being weak and openly admitting to killing her mother. He also shows his sadistic side towards Kyros too when he found out that Scarlet was his wife. Despite his arrogance, Diamante has shown to care a lot about his team and his leader, Doflamingo.
Diamante posses the Hira Hira no Mi which gives him the power to manipulate the density of anything he comes into contact with. With his devil fruit ability, Diamante can make his cape as hard as steel and create ripples in the ground to throw off his target's movement. With his height, size, and stature, Diamante is agile and swift in battle. He is renowned as being an executive officer of the Donquixote Pirates. In the Corrida Colisseum, the majority of the spectators were optimistic that Diamante would be able to defeat the final contestants in the other Blocks despite their abilities.
Many years ago, Diamante was shown to be an early member of the Donquixote Pirates. He was present on Minion Island where it was revealed that Rosinante and Law had betrayed Doflamingo. Diamante and his comrades beat up the Rosinante (who was eventually executed by Doflamingo) and proceeded to find Law who had the Ope Ope no Mi. They could not have found him in time before the massive battle between the Marines and the pirates broke out.
When the Donquixote Pirates managed to invade the Dressrosa and framed King Riku as being the harbringer of destruction, the crew took overthrew the RIku family and became the new royalty of the island. It was revealed later that Diamante was responsible for the killing Scarlet, one of the former princess of Dressrosa and Kyro's wife.
Diamante appears in a meeting alongside Trebol and Pica where Doflamingo was talks about his plan on how to deal with the Law and Straw Hat alliance. He was informed that the Mera Mera no Mi (Ace's devil fruit) was going to be the thing that lure Straw Hat into fighting in the Corrida Colisseum. Diamante later reappears where he was in charge of monitoring the colisseum battles. In the final round, Diamante decided that he was going to battle for the Mera Mera no Mi in honor of the Donquixote Family. During the final round, he confronted Rebecca and revealed that he was the man who was responsible for killing her mother years ago. As the final battle rages on, Sabo took adavantage of the situation and managed to steal the Mera Mera no Mi consuming it in the process.
When the war broke out, Diamante mobilized to the palace where Doflamingo was at. He later waited outside the palace in the sunflower field to confront Rebecca. While attempting to kill her, Diamante turned his attention towards Luffy and Law who were planning to dash to the location where Doflamingo was at. He attempted to stop them but was fooled by Law's Ope Ope no Mi technique. Before putting a fatal blow on Rebecca, an irrated Kyros (who the latter realized as the toy soldier) intervened and challenged Diamante to the fight. While fighting Kyros, Diamante made many attempts to kill Rebecca and gloats about killing Scarlett. As the battle continues, Nico Robin jumps in to protect Rebecca from Diamante while supporting Kyros in his battle. In the midst of the battle, Diamante had the upperhand but Kyros cut him down with his sword which caused him to fall head-first onto a pole marking Scarlett's marked grave knocking him unconscious.
After his defeat, he was captured by the Marines along with the other members of the Donquixote Pirates, excluding Baby 5, and was being escorted to Impel Down.