Mithridates and the Unkillable King
Mithridates VI tried to poison himself—and failed. His own immunity saved him from death, just not by his own hand.

Jacques Louis David — "The Death of Socrates" (1787), public domain
The king who drank poison for breakfast.
Under siege by Rome and betrayed by his own son, Mithridates VI of Pontus turned to his last defense—poison. But after years of swallowing small doses to build immunity, the lethal draught left him alive, choking and humiliated.
Too strong to die—by his own hand.
Ancient sources say Mithridates begged his bodyguard, a Gaul named Bituitus, to end his life. Bituitus obliged. Rome never got to parade the 'poison king' in chains through the streets.
He was killed by his own legend.
Mithridates feared nothing more than a Roman triumph. In the end, he outwitted every assassin—except himself.
After years of dosing himself against every known poison, Mithridates couldn’t kill himself with a simple draught. He had to ask a mercenary to finish the job.