Boros stated that he and his band of pirates "Dark Matter" come from a homeworld with a harsh almost uninhabitable environment. He lead his band of pirates, ravaging planets in his wake, but eventually he became so powerful that he became undefeatable. An alien seer told him of a distant planet where he would find his match, so he scoured the universe for 20 years to find the person who would be his match as told in the prophecy.
Boros is a cyclopean alien who stands over 7ft tall with light pink, spiky hair and bangs that frame his face, sharp teeth and pointed ears adorned with multiple earrings. He has one large blue eye on the centre of his head and light blue skin (in his first form) with blue markings that start from his eye and cover most of his body. He wears golden armour that is designed to suppress his powers, with spikes on his shoulder and forearms and matching curved boots. He also sports a red cape that flows down from his shoulders to the ground. In the manga, his skin at sealed form is of purple colour with darker purple stripes on its face. He also has a red orb on his chest with markings of red and purple on his stomach and arms. He wears baggy white pants, held up by a magenta coloured sash with silver lined purple blades hanging from it.
Like any good dragon ball villain, Boros has multiple forms. His first appearance, of which he's wearing clothes; his second form, which resembles a bug, and his final form, which gives him a white coloration and missing mouth.
Boros' power is overwhelmingly large, so much so that he was the only character in the entirety of the show to survive multiple punches from the titular character, Saitama. While it wasn't seen what he could do with his power suppressing armour on (as Saitama destroyed it in one punch) We definitely can see that he can almost keep up with Saitama to the point where Saitama isn't getting bored (as with Sonic, a fighter whose speed is the main attribute of his character) and upon powering up to his mid form (Dark blue with almost segments body parts) was able to hit Saitama from behind with Saitama seemingly not having time to properly react (although he was only mildly interested in the fight, as always)
His actual physical power is also something that was formidable enough for Saitama to react differently. Upon attacking, Saitama was prompted to block his attacks with his forearm, and during the fight had knocked Saitama through several walls and pillars and the like. He also kneed the titular character hard enough to send him flying to the moon in just a moments time, his impact causing a small crater to form (in his third and final form, being white with blue vein like markings and with minimal facial features left). He was able to keep up with Saitama even when he had lost one of his arms. He also has the most endurance of any villain that Saitama has faced, surviving several punches.
Boros also seems to have the ability to shoot blasts of energy that are devastating. Upon declaring that Saitama had lasted longer than any other who had faced him before (a few minutes into their fight) His chest jewel opens up, revealing a second eye, from which came a blast that Boros described as "The destructive energy within me" and said that "Any normal creature would find even their bones vaporized" He used a super powered version of this, named "Collapsing Star, Roaring Cannon", which he claimed would destroy the entire planet. This attack was powerful enough for Saitama to use his final move "Killer Move: Serious Series...Serious Punch" attack, the only enemy on which Saitama used this move. He also had a "Meteoric Burst" which destroyed a large portion of his enormous ship.
He also possess great regenerative abilities, which allowed him to come back from near complete destruction. Boros claimed that a wound that would be fatal to a normal being would be something he could heal from, and upon stating this regenerated his arm that he lost by focusing his energy on his missing arm. This healing ability seems to be heightened when he reaches his final form, as when he was hit by Saitama's "Consecutive Normal Punches" he was reduced to a splatter, with only his eye remaining recognizable, and he immediately put himself back together. Being in his final form, however, uses a great amount of energy that puts great stress on his body (which he compared to an anaerobic exercise) which shortens his life, so he reserved it for a last ditch effort to defeat an enemy.