The titan of consumption, invincible and unknowable.
"The Eldrazi titans do not dwell in physical space," said Ugin. "They are creatures of the Blind Eternities, and it is in the Eternities that they remain."
"Until they manifest physically, you mean?"
"No," said Ugin. "I meant what I said. Ulamog remains in the Eternities."
"Then what did I see heading toward Sea Gate?"
"You saw a portion of him," said Ugin. "A projection. Imagine that you reach your hand into a pond. The fish below the surface sees a five-headed monster, and cannot perceive the man attached to it. It mistakes a hangnail for an eye because the truth is beyond its imagining. You see?"
"And when you trapped them . . ."
"Like driving a spike through the hand," said Ugin. "The man will not die, but neither will he trouble other ponds. 'Killing' Ulamog's physical form would be like cutting off the hand. The man might be diminished, but he would survive—and he would be freed."
- Uncharted realms article: revelation at the eye.