Any time a new saiyan is added to the Dragon Ball lore fans get incredibly excited. So when Vegeta's brother was introduced to the series, it was a seriously hype moment, even if it took place in a movie that most people never saw.
Vegeta's brother Tarble was introduced in Dragon Ball: The Return of Son Goku and Friends!, a movie that never even got an English dubbed release. It was the first piece of media to be released in the series over a decade after Dragon Ball Z finished airing which makes it all the weirder that it never got a proper western release.
Who Is Tarble, And What Is He Like?
Tarble is a kind-hearted saiyan who lacks the aggression that most of his kind have, similar to Goku's mother Gine. This ends up with his being classified as a low-class saiyan, which is extremely embarrassing for King Vegeta. Because of this, he was banished from the planet, and able to survive Frieza's eventual destruction of his homeworld.
Tarble still has his tail, though he doesn't keep it wrapped closely around his waist as other saiyans do. This might show some lack of aggression in his personality. It's unknown if he can transform into Great Ape form like his brother and father, though logically he should be able to. Tarble also is extremely respectful of his older brother, even though they are obviously a bit estranged.
Tarble's Story
Tarble is a bit like Vegeta, as he eventually ends up in a relationship with an alien woman. Unlike Bulma however, Gure is just as kind and easygoing as her husband, showing that saiyans with less aggression may also not go for stronger women, unlike their counterparts.
Eventually, his peaceful planet is attacked by two henchmen of Frieza, Abo and Cado. As he isn't as strong or adept at fighting as his older brother, he heads to Earth to try and get help from the other saiyans in protecting his homeworld. While Tarble states that he is now as strong as Frieza, this would be him before he was defeated by Goku, showing the rest of the Z-Fighters are now far more powerful.
In the end, it's Trunks and Goten that take on Abo and Cado for the majority of the movie, showing around how strong Tarble is in comparison. Whikle Goku and Vegeta finish off the battle in the end when Abo and Cado fuse together to become Aka, it's quite possible the young children might have been able to finish the job themselves if they had a bit more battle experience. It's also quite possible that the two simply wanted the battle to end as they were both attending a party at the time with the other Z Fighters.
Outside of Dragon Ball: The Return of Son Goku and Friends!, he isn't brought up much more in the series. In Dragon Ball Z: Battle of Gods, he is suggested as an option to help Goku become a Super Saiyan God but the idea is quickly dismissed as Vegeta has no way to contact him, nor does he know what planet he currently resides on.
Dragon Ball Z: Dokkan Battle
Tarble does get a unique side story in the mobile game Dragon Ball Z: Dokkan Battle where he ends up meeting Future Trunks. The two end up fighting each other as Trunks assumes Tarble is an invading saiyan, eventually realizing that he isn't actually evil. Trunks never actually learns that Tarble is his uncle or that they are related at all before Tarble continues on his way to try to find his brother Vegeta.
Is Tarble Actually Canon?
Tarble's status within the canon of Dragon Ball is an extremely complex subject. The movie Dragon Ball: The Return of Son Goku and Friends! Is not itself technically canon within the anime series. Tarble is also mentioned in the Dragon Ball Z: Battle of Gods movie but not in the adaptation of the anime.
To make matters even more complicated, Dragon Ball Super: Broly also mentions Tarble, and it is one of the few movies that is considered canon to the series. While the movies cover the general story arches found in the anime, they tend to be considered canon to the overall story of the series and not necessarily canon to the anime itself, let alone the manga. This is because both mediums can cover the same story with slight differences.
Making things even worse, even if Tarble is considered a canon character due to Dragon Ball Super: Broly mentioning him, it doesn't mean that the events that took place in Dragon Ball: The Return of Son Goku and Friends! Are canon. This means that the canon version of Treble could be entirely different from the one we've seen so far.