Of the members, Yeti and Tygerstryke were original to the program, Rictor joined to take vengeance on Cable for killing his father (actually done by Stryfe), and Grizzly joined as another former member of the Six Pack who had an axe to grind with Cable.
Among the group members, Yeti and Tygerstryke were already part of the program from its inception, Rictor joined to seek vengeance on Cable for killing his father (actually carried out by Stryfe), and Grizzly joined as another former member of the Six Pack who was seeking revenge against Cable.