A hero entered a cave at Tainaron to begin a quest centering on this figure that ended with the third and final instance in which Eurystheus (*)  hid in a jar in fear.
According to Euripides, this character was imprisoned in "the grove of Demeter and the city of Hermione". The aconite plant arose from this character's saliva falling on rocky ground. Hesiod, the first extant source to give this figure a name, describes him as "brazen-voiced". A hero entered a cave at Tainaron to begin a quest centering on this figure that ended with the third and final instance in which Eurystheus (*)  hid in a jar in fear. While searching for this being, that hero failed to save Pirithous but rescued Theseus. While accompanying Aeneas on his  katabasis , the Cumaean Sibyl used a drugged cake to subdue this being. This snake-covered, serpent-tailed being was the target of Heracles's last labor. For 10 points, name this guardian of the gates of Hades, a three-headed dog.
According to Euripides, this character was imprisoned in "the grove of Demeter and the city of Hermione".
Cerberus  [or  Kerberos ]