The Xel'naga are a Lovecraftian-like interdimensional race of titans from the fictional universe of the Starcraft video game.
The Xel'naga are an ancient cosmic race, whom are the universe's most powerful species. Which has conquered worlds and uplifted races, most infamously the zerg and protoss. The reason they uplifted these races was that they were not immortal only incalculably long-lived. Therefore they were planning to use two chosen uplifted race to be create the next generation of Xel'naga.
The originated in the Void, a space or dimension that is separate from the material universe. Which has a breathable atmosphere and has several indigenous species, including the Xel'naga. Every time a new universe was born they took physical form and entered that universe. Where they uplifted races and would eventually be reborn in the next generation of Xel'naga created by the merging of two chosen uplifted races. It's a cycle that was repeated in many universes. In fact it was done so many times that their actions were affecting time itself. The form of the Xel'naga, with many of them having bulbous squid-like bodies. Due to their essence, the Xel'naga and any creatures that contain their essence, would passively bring about the rapid growh of life wherever they are and bring about an explosive growth of fauna and fora, even on dead planets.
Xel'naga refuse to kill anything as they cherish all life. They possessed incredibly powerful psionics, with the most powerful of the Xel'naga being able to literally tear apart worlds. Inside the Void, he also had matter-manipulation powers. Technologically, they were so advanced that to interstellar races, it's function was for all intents and purposes like that of magic. Technology that able to convert material between energy, information, and essence with ease. Xel'naga built spacecraft and orbiting space platforms, artificial constructs, artifacts that can control minds, and artificial intelligence. Some of their artifacts would not be damaged by conventional weaponry.
Recently a rogue faction of Xel'naga led by Amon, tired of the cycle, sabatoged everything and brought about the ruin of the Xel'naga. In their desire to bring about a new perfect universe without the Infinite Cycle (the process of uplifting races and creating new generations of Xel'naga), they corrupted one of the uplifted species, the Zerg. The other Xel'naga discovered his betrayal and waged war against Amon and his followers. Amon unleashed upon his kind the Zerg who consumed most of the Xel'naga. He was destroyed by the last of the Xel'naga, though his consciousness escaped to the Void where he waited for his return. The few remaining Xel'naga likewise returned to the Void. Millennia later Amon would return to the material universe, influencing various individuals, factions, and races in his bid to finish his work.