Iolaus was the Greek hero who helped Heracles by cauterizing the Hydra’s severed neck stumps.
During Heracles’ second labor, he fought the Lernaean Hydra, a serpent-like monster whose heads could multiply when cut off. Heracles discovered that ordinary decapitation was ineffective because new heads grew from the open wounds.
His nephew and companion Iolaus solved the problem by using fire to burn, or cauterize, each stump immediately after Heracles cut off a head. This prevented regeneration and allowed Heracles to continue the battle. Heracles then buried the Hydra’s immortal head beneath a heavy rock and dipped his arrows in its poisonous blood.
The myth varies in details: ancient sources disagree about the Hydra’s exact number of heads, and some versions give Heracles more direct responsibility for the burning. Still, Iolaus is the canonical assistant in the familiar account, not Theseus, Telamon, or Peleus.