General Grievous

Grievous was a General and the Supreme Commander of the Separatist Droid Armies during the Clone Wars. He claimed to have became a cyborg to become stronger and replaced his arms with cybernetic ones that split into two, giving him four arms, however he in reality became a cyborg due to an accident, where he lost much of his organic body. Count Dooku trained him in Lightsaber combat and made him a General in the Separatist Armies. So many people think that Grievous is a droid, but he is not.