The Hulkbusters are a special United States Military unit that operates on capturing or possibly destroy the Hulk. They're led by General Ross.
The Hulkbusters possess the most advanced weapons and vehicles at their disposal to combat the Hulk wherever he shows up. The Hulkbuster Tank, Hulkbuster Attack Chopper, and the Hulkbuster Command Vehicle are the examples of their arsenal.
The Hulkbusters under General Ross has been hunting down the Hulk/Banner for months now. They finally spotted the Hulk in Las Vegas as the latter fights the Absorbing Man. All of their Hulkbuster forces has engaged them after the Hulk finishes off the Absorbing Man. The Hulk defeated them but didn't kill Ross's men in the battle. All of their Hulkbuster Tanks and Attack Choppers were destroyed leaving only the Hulkbuster Command Vehicle left where Ross is.
As the Hulk is about to finish them off, he was stopped by two S.H.I.E.L.D. agents, Black Widow and Hawkeye who were also on a mission to capture him too. As the baatle ensues between the Hulk and the two agents, Ross was enraged that S.H.I.E.L.D. was interferring in his mission to capture the Hulk. So he decided to fire a large missile at the Hulk, not caring about harming the agents in the explosion. Unfortunately, the Hulk just saved them by colliding himself with the missile so the two will not be hurt. After the explosion, the Hulk was thrown into the mountain causing it to collaspe on the S.H.I.E.L.D shuttle. The Hulk was about to escape but hesitates and saves the shuttle from crashing. Then he was captured by the two whom he saved and was transported to the Cube. The Hulkbuster was ordered to stand down after Hulk's capture much to Ross's anger.
As soon after the Breakout, the Hulkbusters was on the move again to recapture the Hulk again. Their Hulkbuster units were seen attempting to get him but were told to stand down due to the Avengers protecting him. They cannot get the Hulk because he's in the Avengers and if they want him, they'll have to get through his teammates.
After the Hulk left the team, the Hulkbusters were on the pursuit again. They finally spotted and engaged him in the forest region. They almost had him until Hawkeye swoops down and saves him. They were forced to retreat.