The Alliance of Evil is a quartet of sinister villains who seek to eliminate the SWAT Kats and finally take over Megakat City. These evildoers who formed this group are Dark Kat, Dr. Viper and the Metallikats.
When Dark Kat crossed Dr. Viper in their mutual pursuit of Katalyst 100, Dark Kat suggested that instead of fighting each other they confront their common enemies together: the SWAT Kats. They then stole the remains of the Metallikats from an Enforcer evidence locker and rebuit them, attaching neuro-scramblers to ensure the robots’ loyalties.
The alliance was unstable at best, as the defiance of the Metallikats, the abuses and treachery of Dark Kat and the conspiring of Dr. Viper worked to undermine their own goals, despite together having destroyed the Turbokat and capturing the SWAT Kats along with Mayor Manx and Deputy Mayor Briggs. Ultimately the alliance fell apart as they were their own worst enemies.