The Hydra, in Greek mythology, is the offspring of Typhon and Echidna and a gigantic monster with nine heads (the number varies), with the centre one being immortal. The monster’s haunt was the marshes of Lerna near Argos. The destruction of Hydra was one of the 12 Labours of Heracles, which he accomplished with the assistance of Iolaus.
As one head was cut off, two grew in its place. Therefore, Iolaus finally burned out the roots with firebrands as soon as Heracles cut off each head.
At last Heracles severed the one immortal head from the body and buried it under a heavy rock. The arrows dipped by Heracles in the poisonous blood or gall inflicted fatal wounds, eventually including his own accidental death at the hands of his wife, Deianira.