The Many-Angled Ones are a race of eldritch abominations that infest entire universes with life until they being pushing outwards onto other realities. Doctor Strange villain, Shuma-Gorath, is believed to be among their ranks. They appear as a writhing mass of flesh with eyes, maws and tentacles, though whether this is their true form or something they can manifest as is not known.
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.