Same Old Barney
Clint Barton's brother Barney was his best friend and protector growing up. He taught Clint how to fight and ran away to the circus with him. Barney and Clint's relationship was strained after they joined the circus. Clint wanted to become a part of the show while Barney saw it only as a way to make ends meet. The two grew distant and when Barney left the circus to join the army he was forced to leave Clint behind.
When they next met Barney, by then an FBI agent was working undercover. Clint shot him on a mission, an accident that led him to leave his mentor's influence. When they met again Barney asked Clint, then an Avenger help stop a racketeering ring. He was successful but it nearly cost Barney his life.
From there Barney fell prey to the wrong crowd. Baron Zemo manipulated him to turn against his brother and the two became rivals for a time. Barney was recruited by the Dark Avengers to play the role of their Hawkeye. Despite this he continued to support his little brother in small ways. In Hawkeye: Blindshot he provided a bone marrow sample that allowed Tony Stark to give Clint a transplant that would save his eyesight. Barney claimed his altruism was only in an effort to get Clint battle ready so they could fight once more.
Barney and Clint eventually became close again after Barney left the Dark Avengers. He started living on the streets and eventually found his way back to Clint. Clint welcomed Barney into his life with open arms and for a time they made quite the team. Barney helped his brother defeat the tracksuit mafia to his own detriment when he was laid up in a wheelchair with minor injuries. He also made every effort to help Clint recover from his own injuries, a head wound that claimed his hearing once more.
In the aftermath of the battle however, Barney used it as an opportunity to take back money Clint had won from him years earlier as well as one of Clint's tenants. He bought an island where he started to lay down roots. The work he made to reconcile with Clint for past gripes didn't go to waste though. Despite the money he took from Clint the younger Barton continues to seek out his brother's advice and counsel.