Sabo is the Chief of Staff of the Revolutionary Army, and is recognized as the "No. 2" of the entire organization, being directly under Dragon himself in terms of command. He is an adoptive brother of Luffy and Ace, and the son of Outlook III.He was born into a noble family in the Goa Kingdom but decided to run away and live in the Gray Terminal, eventually setting out to sea on his own. 12 years before the present storyline, he was a childhood friend of Ace, and eventually Luffy as well, to the point where the three considered themselves to be "brothers", swearing an oath of brotherhood over sake. Along with Ace and Luffy, Sabo's dream was to become a pirate so that he could set sail and achieve freedom, and made plans with his brothers to set sail at age 17.
Despite this, Sabo decided to set sail before Ace and Luffy, and his boat was destroyed by a Celestial Dragon moments later. Sabo was believed to have died from this event, but survived after being saved by Dragon and joined the Revolutionaries. Sabo lost most of his memories from that point forward, but regained them after learning that his adopted brother Ace was killed at Marineford. Sabo was a ten year old boy at the time of Luffy's flashback, the same age as Ace at that time. He had a missing tooth and short curly blond hair. He wore a large black top hat with a pair of blue goggles wrapped around it, a blue jacket with the sleeves rolled up, a cravat and a pair of light blue cyan shorts held up by a belt with an elaborate flower-design buckle. Before he entered into the Gray Terminal, he was seen with a gentle outfit with a white colored short-sleeved shirt and wearing blue colored shorts as usual. As an adult, Sabo became taller and more muscular. He has matured greatly, with more pronounced facial symmetry and a scar he acquired over his left eye. This scar was inflicted when Saint Jalmack selfishly blew up the fishing boat Sabo used to set out to sea, leaving him with serious burns and critical injuries. He resembles Luffy enough to allow him to easily deceive opponents as perceptive as Diamante into thinking he was "Lucy" by simply wearing the same outfit, although Sabo is still taller than his younger brother. His hair has also grown noticeably longer since his youth. While participating in the final round at the Corrida Colosseum in Luffy's place, he wore Luffy's cape, fake beard, and viking style helmet. In addition, he wore shades to conceal his eyes. He also drew an x-shaped mark on his chest. Later, after the round, he returned to his original outfit, which resembles his old outfit from twelve years ago: a long black jacket with a buckle on the left sleeve, with a blue shirt and vest, a frilled cravat, and a simple belt holding a pair of loosen light-blue pants with black boots (said boots are shown in greater detail in Pirate Warriors 3, to be wrapped with buckles and with cloth bracings). He also wears a pair of brown gloves and the same top hat with goggles over the band.
Sabo is devoted to his dreams to the point that he agreed with Ace that the two of them had to kill Luffy so that he could not tell anyone about their treasure, though neither Ace nor Sabo knew how to kill a person nor had any experience, implying some degree of innocence despite their profession. He is very ashamed of being a noble, and even stated that he wished that he hadn't been born as one. According to Luffy, Sabo is a nicer older brother than Ace. He acknowledged Luffy's powers, and even encouraged his improvement. He helped Ace and Luffy get along when they were fighting, thus being the nice, diplomatic one of the trio. Sabo's dream involves traveling around the world as a pirate. This is in order to write a book containing the story of everything he would see and every place he would visit during his journey. One of the reasons behind all this could be the "segregation" that envelopes so much of the Goa Kingdom, a thing that could easily stir a freedom-loving spirit like Sabo's to ask himself what the world was really like outside the walls of High Town, and outside the island itself. However, he was ready to cast aside his dream for the sake of his loved ones. Sabo was loyal to his friends and, in this case his two "brothers", to the point that he would give in to the demands of his father, becoming miserable and "alone" in order to save both Luffy and Ace. Despite being the son of a noble, Sabo does not act like a stereotypical noble would act, nor does he consider himself to be a noble. He does not look down on the less fortunate nor does he put on airs about his status. This is in stark contrast to the rest of his family, who see their status as more important than anything else and will do whatever it takes to raise their social standing or maintain their current status, as well as look down on anyone they consider to be inferior. Sabo rejects these values completely, and even went as far as to say that he feels ashamed of his status as a noble. This can be seen as the reason why he ran away from home and went to live in the Gray Terminal, forfeiting his noble heritage. Since a child becomes a full-fledged noble at the age of eighteen, Sabo intended to leave the Goa Kingdom at the age of seventeen, to escape the idea of being recognized as the thing he hated the most. He even refers to the nobles as "smelling worse than Trash Mountain, as they are people rotten to the core". At age 22, Sabo has retained much of his old personality, although he appears to have adapted many mannerisms from Luffy, including his brother's tendency to mispronounce the names of others. He has also displayed an immensely fierce protective streak towards Luffy, to the point where he disregards everything he is currently doing if he feels Luffy is in danger, including his duties in the Revolutionary Army; his tendency to hang up the phone in the middle of a call rather angers his comrades. This is largely contributed by Sabo's inability to protect Ace from death, a fact he still regrets to this very day. This is ironic considering that Ace himself had gained a very similar protective-streak after Sabo's presumed death.