Iolaus helped Hercules defeat the Lernaean Hydra during Hercules’ second labor.
As Hercules cut off the Hydra’s heads, new heads grew back from the wounds. Iolaus solved this problem by cauterizing each neck with a burning brand, preventing further heads from emerging. Hercules then buried the monster’s immortal head beneath a heavy rock and used its poisonous blood on his arrows.
Iolaus was Hercules’ nephew and a trusted companion. He was the son of Iphicles, Hercules’ mortal twin brother, and was frequently portrayed as assisting the hero in dangerous adventures. Some ancient traditions even describe him as Hercules’ charioteer.
A common mix-up is to credit Athena with directly defeating the Hydra. Athena gave Hercules useful advice in some versions of his adventures, but Iolaus performed the crucial task of burning the Hydra’s necks. Because Iolaus assisted Hercules, Eurystheus later refused to count this labor fully in some accounts.