He is a homeless and idiotic Garo who used to live in the sewers under Ganondorf's castle for over 500 years until he became part of SMG4's Gang and the best friend of Fishy Boopkins, moving into the Mushroom Kingdom. Throughout most of his time, Bob was selfish and was secretly aiming to be famous, acting like a showoff, and mentally looked down at his friends. He also acts antagonistic at times, such as in SMG4: Mario's Train Trip.
In Season 8, his selfish dreams of fame eventually drive him to become the titular main antagonist of The Rapper Bob Arc, orchestrating events that would make him the greatest rapper, but his old friends manage to steal his popularity and abandoned him for some time. Thanks to Waluigi (the previous arc villain), he redeems himself and reconciles with his friends, and joined them on many adventures.
In this episode, he helps Mario do his work at the Circus, though it ends up badly for him. He then saves Mario from Waluigi, but after he accidentally shoots a baby doll at Donkey Kong, Bob ends up getting mauled.
Bob displays his selfishness by choosing to abandon Mario and Luigi to the horde of T-Posers, which eventually resulted in Luigi infected by the T-Pose Zombies. As retribution, Mario threw him off the roof. As Bob clings onto the edge of the roof with Mario standing over him, Bob claims he was joking and that "it was just a prank bro". Pissed, Mario flips him off and kicks him off the roof and into the swarm of T-Pose Zombies, presumably infected.
One day, the Earth was blessed with the sexiest man on Earth. Upon seeing him, they could not bear his sexiness and exploded. Bob then went on to save the world and get all the bitches.
Bob is a selfish, attention-hogging, foul-mouthed, and sometimes cruel Garo. He loves himself more than anyone and believes he is far more important in the world than anyone else. In fact, he made himself a really long fake autobiography where he defeats SMG4 (who was apparently the book's main antagonist) and replaced him as the new main character "forever and ever". In both the same book and his Soundcloud account, he believes to be "the sexiest man in the world". This led to SMG4 branding him an "asshole". He also sometimes leaves his friends to die in certain situations (such as the first T-Pose outbreak) despite their begging, which infuriated Mario, as this led to Luigi being transformed into a T-Pose zombie.
Despite that though, Bob really did care for his friends aside from the Rapper Bob arc, considering the fact he hasn't seen anyone for 500 years and called Boopkins his best friend during the Purge. However, at some point, he started seeing his friends as morons who only made his life "devastating", and used them to selfishly gain fame. Upon Boopkins accidentally ruining his concert, Bob angrily revealed that he never considered Boopkins nor anyone else his friend, and upon rebuilding his career, he proceeded to humiliate not only Boopkins but all of his friends on live TV. However, after his career was ruined by his former friends, Bob tried and failed to make amends with them, until Waluigi made him realize that his friends were the most important thing to him. He eventually decided to stop being a selfish narcissist and became friends with Boopkins and the others again, supposedly.
Like Luigi and Tari, Bob is an immense coward, terrified of death, and often begging or bargaining for his life, which is shown strongly in SMG4: The Mario Purge. In that same video, he tried exaggerating his bravery to the Teletubbies who captured him and his friends to get them to free him, to no avail.
As revealed in Mario's Challenge and basically every episode he appears in, he has a bad sense of humor that only annoys people, which led to Gobbles The Gargoyle crushing him. The only time people laugh at him is when he is in pain.
SMG4: Smart Mario indicates that Bob is an idiot, being nearly as dumb as Mario despite the fact that he is good at scheming.
Assault: Bob occasionally assaulted people, the most recent example being Mario in The Mario Concert.
Holding Hostages: In Trick Or Treat Wars, Bob, fed up with not getting any candy, proceeded to grab a gun and held people hostage, threatening to kill them if they didn't give him any candy. This led to the police arresting him.
Threatening: In The Mario Concert, he told Mario and Luigi to be in his luggage but they refused. He then hold a gun, threatening to shoot them if they didn't get it.
Bob is an expert on garbage, as he has a degree in garbology (the study of garbage), mostly because Bob is a professional piece of garbage.
In his first appearances (mostly in 2017), Bob's singing talents were downright awful, to the point where there was a whole challenge dedicated to it in War of the Fat Italians, probably due to his text-to-speech voice. In 2018, however, Bob's talents have apparently improved, as people no longer cringe and get mad when hearing it.
He likely swears more than any other character considering he had a challenge where he had to not swear for 10 minutes. Obviously, Bob failed.
From The Smash 5 Trials, Bob had not showered in 24 years. However, people do not complain that he smells bad.
Bob's model is a Garo from The Legend Of Zelda: Majora's Mask. Apparently, Garos are spirits of ninjas who usually spy on the Ikana Kingdom, which according to a ghost, only the dead roam.
This is just speculation, but perhaps this is why Bob is at least 500 years old.
Bob's voice comes from the free online text to speech service Acapelagroup, where his voice is labeled as WillFromAfar.
This voice is most well known for the phrase "We are in the beam!" which was said in the Update: Invasion in Team Fortress 2.
However, as of recent videos, people have started to become more accepting of him.
There are several trivia related to Hobo Theatre: THE ORIGINS OF BOB:
When Bob's stolen computer breaks, Luke Lerdwichagul makes a side comment, "At least I learned Russian." as Bob's persona, suggested that Bob learned Russian from playing Counter-Strike: Global Offense.
Bob is supposed to have originated as a trash bag that was accidentally put in a toxic waste field by Wario. However, this makes no sense unless Wario was taking out the garbage and that he had time traveled due to Bob being 502 years old or he can only be that older 507 years old for his own age.
Bob appears to be a replacement for SMG69. They both are fans of SMG4 and frequently ask him to be in his bloopers, yet SMG4 keeps refusing, although SMG69 only once appeared outside of videos involving blooper production. He appeared in Ssenmodnar 8, where SMG69 asks SMG4 to be in a video before SMG4 throws him into the sun, killing him off. It is possible that this is the reason Bob replaced him.
According to (fan-contributed) closed captions, Bob's speaking subtitles use alternate typesetting of uppercase and lowercase text that represents a mocking tone.
In Mario's Train Trip, he claims that he has a final form, but when pulling the lever to activate it, he just disconnects the train car at the back of the train so that he may have been lying.
However, Mario and the Anime Challenge suggests that Bob may be more powerful than we think, as in the Goku Scream challenge, he becomes a Super Saiyan 3, and during the final anime battle, Bob uses a Kame-hame-ha attack from Dragon Ball, which he states is only 2% of his power.
Starting with War Of The Fat Italians 2018, Bob's eyes are now more expressive but they started having expressions back in SMG4: Mario University wherein a picture, he had angry eyes.
In The Mario Purge, Bob claims that he knows Jiu Jitsu in the military although once again, he could just be exaggerating.
In Mad Mario Bob is angry at the internet drought because he needs his daily dose of boobies, hinting he watches porn.
In Mario and the Bob Mansion..., it is revealed Bob refers to Thanksgiving as "Bobsgiving" and Christmas as "Bobmas". This is apparent due to his selfish demeanor and in that instance, as a way to scam as well.
He is the second SMG4 character to get their own arc, the first being Waluigi.
Coincidentally, both of them were antagonists of their respective arcs.