The Many-Angled Ones are a race of eldritch abominations.
The Many-Angled Ones are Lovecraftian horrors, beings of Chaos. They live in the void between the universes of the Multiverse. It has not yet been revealed as to where or how they originated, but they have been around for hundreds of millions of years. One theory is that just as demons were created from the nightmares of mortals, so were the Many-Angled Ones created by the nightmares of demons.
The ruler of the Many-Angled Ones, Shuma-Gorath, has stated that he has been around since the beginning of the universe which would imply that not only is the race billions of years old but that they preceded the demons. They appear as a writhing mass of flesh with eyes, maws and tentacles. It is known that Shuma-Gorath himself does not actually have a body, what others see is simply a shell containing his essence. They are worshiped on countless worlds and dimensions throughout the Multiverse, and every world or dimension that they have conquered is one that is now decaying and dying.
In an alternate universe, the Many-Angled Ones were able to save a dying Captain Mar-vell and have him swear his allegiance to them. They were also able to defeat the Death of that universe, meaning that nothing was able to die. Eventually this reality came into contact with the 616 universe through the Fault, a rip in space and time.
The threat of the Many-Angled Ones was such that cosmic entities like Galactus and the Celestials came to fend off the threat from the other side of the Fault. Eventually, the Many-Angled Ones sent a weapon known as the Galactus Engine through the Fault, which was so powerful that it could overpower the Galactus of the 616 universe with ease, and also dwarfed him in size. It was said that the creatures that were pushing it through were even more powerful.
The Many-Angled Ones were seemingly defeated when Thanos, the Mad Titan, allowed Mar-vell to kill him, drawing the 616 Death to that universe and wiping it of all life, though it is likely these powerful monstrosities survived.
The greatest of the Many-Angled Ones is Shuma-Gorath. To mortals he appears as a giant Lovecraftian horror, a giant eye in a lump of flesh surrounded by long tentacles. In it's home chaotic dimension, he is an omnipotent god. Fortunately, it is only able to send a sliver of its essence into other realities. Therefore though he is all powerful and incomprehensibly vast in his home, in other realities he only has a tiny fraction of his power and he is usually the size of a multi-story building.
If Shuma-Gorath was to appear in one's universe, the pressure from his aura would destroy many galaxies. From his home dimension he is able to transmutate worlds in other realities, create minions, and bestow powers. The limits of what Shuma-Gorath can do in other realities with his mystical powers is unknown. When he gathers his powers, he can create a ball of energy with which he can destroy a universe.