The "gang" term comes from the "Gang of Four," a Chinese political faction that abruptly and dramatically lost power in the 1970s. American politicians adapted the phrase for their own purposes.
The "Gang of Seven" was a group Republican freshmen who entered the House in the 1990 election and went on the attack over congressional ethics. They included John Boehner (R-OH), who is now Speaker of the House.
The "Gang of Fourteen" was a bipartisan group of senators who helped avert a 2005 crisis over judicial filibusters. One member was John Warner of Virginia, no relation to his Democratic successor, Mark Warner.
In 2009, a different "Gang of Six" sought bipartisan Senate agreement on health care.