In the Judge Dredd story "The Day the Law Died!", the insane tyrant Judge Cal hires a group of Kleggs to put down a revolution by massacring hundreds of citizens and garrison Mega-City One to terrorise the citizens with their "Klegg-Hounds" (who are alien beasts that look like large dogs with heads of crocodiles and hunt by tasting the ground their pray has stood on). Their battle-cry was "Klegg-Hai! Klegg-Hai!" and they also preceded this with a war-song: "slicey slicey, oncey twicey, claw and fang'll kill Dredd nicely! Meaty beaty, chop 'em neatly, death or glory no retreatee!". The tyrant Judge Cal also place the leader of the group, Grampus , as Deputy Chief Judge of Mega-City One after the assassination of Deputy Chief Judge Goldfish.
After Judge Cal plans to release the toxic gas which will wipe out Mega-City One, killing 800 million people, Cal gives the Kleggs their payment and allows them to leave but when Dredd and the loyal Judges battle them, the Kleggs attempted to surrender but they were mercilessly shot down in retaliation for massacring numerous innocent people.
After the death of Judge Cal, the Kleggs were banned from Mega-City One and any citizen that encounters a Klegg are required either to kill it or inform the Judges immediately so they can do the work. Due to the hateful memories of the Kleggs, other more peaceful aliens have been less than welcomed in Mega-City One.
The space-set spin off The Corpse features a brutal war of attrition between Mega-City One's Space Corps and the Klegg Empire in the Spiral Arm, and the Kleggs signed a peace treaty with Sino-Cit, with "peace fort" bases at the Kaeli moons that divided Klegg and Sinese space.
Later strips and spin-off books have used the Kleggs as recurring mercenary characters. Other looks at the Klegg Empire itself included a one-off spinoff, The Kleggs!, where an education was rare and only for those born into the ruling high ; rule of the Empire was gained through "time honoured traditions of backstabbing and treachery", and in 2124 Chorr took command from his uncle Grand Warmaster Grusk after an accident with an alien superweapon. In 2132, warlord Skull Khan Kirrz was on a war crime trial for committing the Edgeworld Marches atrocities.