Approach the inactive Runic Golem in one of the side-chambers in the Deep Roads Grotto.
After interacting with the golem, Jerrik Dace will muse that there must be a control rod nearby. Upon leaving the golem's chamber, the mist will have shifted once again, revealing another chamber with the control rod and a Rune Anvil in it. After battling four shrieks, pick up the control rod, return to the golem and activate it.
The Runic Golem re-activates and becomes an incredibly hardy companion.