Save the Ogre is a side quest in The Darkspawn Chronicles DLC for Dragon Age: Origins. It is available as part of the main quest Storm the Gates. Rescue the wounded ogre from the crossbowmen that have it surrounded and then recruit it as your thrall.
Once you have completed Earn Respect in Battle and cleared the area of enemies, head to the marker in the center of the map. There you will find the ogre near a set of barricades and several crossbowmen. Once all the crossbowman are defeated, cast Enthrall on the ogre to recruit it.
The Ogre (thrall) is now a member of your party.