Bartolomeo, also known by his epithet "Bartolomeo the Cannibal," is a pirate who serves as the captain of the Barto Club and later becomes the leader of the second ship of the Straw Hat Grand Fleet. He hails from Loguetown in the East Blue, where he was originally a notorious crime boss controlling over 150 towns. His entire life changed when he witnessed the pirate Monkey D. Luffy’s daring escape from execution at the hands of Buggy the Clown. Seeing Luffy smile fearlessly on the scaffold before a bolt of lightning miraculously struck the platform, Bartolomeo became convinced that Luffy would become the Pirate King. Inspired by this event, he abandoned his life as a gangster, collected every news story about Luffy’s exploits, and ultimately set out to sea to become a pirate.

Bartolomeo’s personality is a striking contradiction of extremes. He is widely known as a ruthless and violent criminal, having committed acts such as bombing and burning civilian cities and distributing snuff films of tortured pirates. This behavior has earned him the number one spot on the public's "Most Wanted Pirate to Disappear" list. He is vulgar, laid-back, and often displays provocative behavior, such as taunting crowds and urinating in public in a fighting arena. He openly voices his disgust for what he perceives as selfish human nature. However, this cruel demeanor masks a profound sense of loyalty and honor. Bartolomeo cares deeply for his crewmates and will go to great lengths to protect them. He also refuses to stand by while a friend is in danger, even if that friend was a former enemy.

The core of Bartolomeo’s motivation is his fanatical devotion to the Straw Hat Pirates, particularly to Luffy. He refers to every member of the crew with the honorific "-senpai" and becomes overwhelmingly shy, nervous, and prone to fainting when in their presence. He views the Straw Hats not just as idols but as the epitome of everything a pirate should be. His primary goal in the Dressrosa story arc was to win the Flame-Flame Fruit at the Corrida Colosseum specifically to present it to Luffy as a gift. He becomes enraged and violently attacks anyone who insults Luffy or speaks ill of the Straw Hats, demonstrating that his admiration is backed by genuine, aggressive conviction.

In the overall story, Bartolomeo plays the role of a powerful ally to the Straw Hat crew. He makes his major debut as a gladiator in the Colosseum, where he easily wins his block by using his powers to withstand the legendary King Punch of Elizabello II. After pledging his loyalty to Luffy, he becomes a key player in the ensuing battle against the Donquixote Pirates in Dressrosa. He uses his unique abilities to protect Luffy's companions, including Usopp and Robin, and works alongside the pirate Cavendish to defeat the executive Gladius. Following the defeat of Doflamingo, Bartolomeo is one of the seven pirate representatives who drink the "sake of brotherhood," officially forming the Straw Hat Grand Fleet, with his own Barto Club becoming its second division.

Bartolomeo’s key relationships are almost entirely defined by his admiration for the Straw Hats. His most significant bond is with Monkey D. Luffy, his hero, for whom he is willing to sacrifice everything. He also develops a strong respect for Sabo upon learning of his connection to Luffy, calling him "great senpai". While he works well with Cavendish in combat, their relationship is a bickering rivalry similar to that of the Straw Hats' own Roronoa Zoro and Sanji. He shows a surprising sense of camaraderie towards Bellamy, saving his life because they fought together in the Colosseum. His loyalty is put to the test later when he enters a territory of the Four Emperors, Shanks. Ignorant of Shanks’s connection to Luffy, Bartolomeo burns the Red Hair Pirates' flag to promote the Straw Hats, leading to a confrontation where he proves his absolute loyalty by willingly drinking what he believes is poison.

As a character, Bartolomeo develops from a simple, feared super-rookie into a dedicated subordinate of Luffy's growing fleet. While his core personality remains unchanged, his role solidifies from a solo act into a captain who proudly flies the Straw Hat flag and works to spread their name across the New World. His journey shows a man who once used his power for criminal chaos now channeling that same destructive energy into fierce, devoted protection for his heroes.

Bartolomeo possesses notable abilities, primarily as a Devil Fruit user who ate the Bari Bari no Mi, a Paramecia-type fruit that allows him to create barriers. By crossing his fingers, he can generate near-indestructible transparent barriers. These barriers have been shown to withstand incredibly powerful attacks, including the King Punch said to be capable of felling a Yonko, the slashing attacks of Hakuba, and even the crushing pressure of Doflamingo's Birdcage. The limitations of his power are that he can only create one barrier at a time, the total surface area he can generate is limited, and the barriers cannot block sound-based attacks. If his fingers are prevented from crossing, he cannot activate his power. He has creatively used his fruit in combat for both defense and offense. Techniques include Barrier Crash, where he propels a barrier forward like a projectile; Barrier Bull, which surrounds him like a bulldozer to push enemies away; Barrier Sphere, which encloses a target; and Barrier Pistol, a punch covered by a small barrier as an homage to Luffy's signature attack.