The Dark Avengers is the unofficial name for Earth's Mightiest Heroes when they were gathered and controlled by Norman Osborn. When he first took control of the Avengers and the Initiative, Osborn reconstructed the team out of members who were loyal to him, or could be properly manipulated. During the Dark Reign, they were active in Dark Avengers #1-16, until Osborn was dethroned in Siege.
Osborn later returned and restarted HAMMER in a public relations conflict against SHIELD and Captain America's Avengers. He recreated the Dark Avengers to oppose his enemies at the same time.