From Haaren's Famous Men of Rome biography of Gaius Mucius Scaevolus.

[Note : The man whom Haaren refers to as Gaius Mucius Scaevolus is generally known as Gaius Mucius Scaevola.] Romans were often known by nicknames earned through exceptional deeds, like Scipio Africanus or for outstanding facial features like Ovidius Naso (nose). Gaius Mucius Scaevolus earned his nickname Scaevolus (left-handed) for the deed of daring he performed to save his country.

After Gaius Mucius Scaevolus botched an attempt to kill King Porsena of the Etruscans, he was captured and ordered to reveal which other Romans were plotting assassination. Instead of answering, Gaius Mucius Scaevolus lost the use of his right hand by thrusting it in a nearby flame to demonstrate to the king Roman contempt for pain or torture.

Impressed, King Porsena freed Gaius Mucius Scaevolus who, once free, voluntarily revealed the plots' co-conspirators.

Terrified by the details, Porsena immediately made peace with Rome.