The Other serves Thanos, who is helping Loki Laufeyson. When Loki has arrived on Earth, Thanos is contacted by him, and the Other threatens the God of Mischief, declaring that if he fails in defeating the Earthlings, Thanos will make him know a new kind of suffering.
When eventually Loki is defeated, the Other complains to Thanos that the Earth's inhabitants are not as weak as they were supposed to be, he declares that challenging the Earth's heroes would be to court Death. To this, Thanos simply smiles.
When Gamora betrayed Ronan and Thanos, the Other summoned Ronan and Nebula to Thanos' domain to discuss the betrayal. Ronan got into a heated argument with the Other and used the power of the Universal Weapon to snap the Other's neck, killing him instantly.
After a few years once Thanos retrieves the Infinity stones, he brings the Other back as a reward for his loyalty.