Drixco

Drixco was once a low caste industrial drone. He honed his battle skills in the Blaster City arenas, then joined Megatron's Decepticons when the war began. He is of note only due to the nature of his death. Drixco was the first Decepticon Optimus Prime ever killed, and the act sealed the young Autobot Commander's commitment to the war.

Exodus
During the Siege of the Hydrax Plateau Drixco was busy carving his way through Autobots with his vibroblade skills when he happened upon Optimus Prime. He had just killed an Autobot who had once been a worker at Six Lasers Over Cybertron when he saw and leaped at Prime. Prime leveled his gun and blew the sword-wielding Decepticon to pieces without ever knowing his name. The act both forced Prime to question his part in the war and, in the end, hardened his commitment to the path he had chosen.

Trivia

 * He is the first victim of Optimus Prime.