Capture and bring back Cerberus.

Cerberus was a three-headed dog. This monster was guarding entrance the land of the dead. Eurystheus sent Heracles to captue this mythical animal.

Hermes and Athena helped Zeus's son with his labour. In that time Heracles was in the underworld.

Hero showed Cerberus to Eurystheus and brought it back. After twelfth labour Eurystheus let Heracles go.

So, Heracles did his last labour.