Marvel Comics UK continuity
During a time immediately prior to the Cybertronian Civil Wars, the planet was broken up into a gala of warring city-states, ruled over (rather pathetically) by the last of the Autobot Overlords. This aging, rusted husk of a mech—enfeebled to the point of needing a near-constant supply of Energon injected directly into his body to keep himself functional—had attempted to quell the fighting between two such providences, those of Tarn and Vos, with the suggestion of settling their disputes through gladiatorial combat, instead of all-out conflict. The talks went sour, however, and as war began brewing between the two city-states once again, the Overlord—accompanied by his trusted bodyguards Nightstalker and Ravage, along with Optimus Prime and a then-neutral Megatron—was forced to beat a hasty retreat back to Iacon.
He didn't get far, however, before the Tarn forces cornered him and his party at the ruins of the bridge to Iacon, the forces having demolished it to prevent their quarry from escaping. Jumping the gap, Optimus went on ahead to gather reinforcements, while Megatron and the bodyguards held their ground. Unfortunately, they quickly realized just how outnumbered they really were, and both Megatron and Ravage suggested they try to jump the gap, as well. Nightstalker, in an extreme show of loyalty to his charge, defied their suggestion and sacrificed himself to take out the Tarn army, instead of leaving the Overlord behind to save their own skins.
His sacrifice was in vain; now almost completely out of energon, the Overlord pleaded to both Megatron and Ravage to spare some of their own energy to keep him alive, but they rebuffed him. Megatron was convinced that he would make a better leader of Cybertron even then, and Ravage was convinced to agree, noting that Megatron was the planet's best chance of weathering the inevitable change on the horizon. Faced with this shocking betrayal of his most trusted comrades, the Overlord was left to perish, his death retold by Megatron to all who asked as his circuits giving out from the stresses of escaping the Tarn army.