Short answer: He/it is a Great Old One form the Far Realm.
Longer answer: He/it is a star infested by magic from the far Realm that wanders the space around the material planes and is slowly dying and wants to feed on the mortals of the various material planes. He/it is a patron to Warlocks ofr the most part.
Edit: apparently the Neogi (form Volo's Guide to Monsters) are particularly adept at contact hi/it and getting power.
Hadar, The Dark Hunger, The Craven Star. It is to my knowledge that Hadar is star that was corrupted by the influence of ancient aboleth lords. This caused it to form an ego, and either in an attempt to avert it's own destruction or to spread entropic nothingness, they seek to consume all that there is. Thus, spells that sport the name Hadar are often ones that try to bring a modicum of the entity to the caster's location so that it may render what crosses paths with it to ruin. The D&D 5e stream, High Rollers, had taken the concept of Hadar and merged it with that of an nigh unstoppable black hole, their similarities are notable after all.
I've seen spells referencing Hadar but I can't find anything on who or what Hadar is?
Short answer: He/it is a Great Old One form the Far Realm.
Longer answer: He/it is a star infested by magic from the far Realm that wanders the space around the material planes and is slowly dying and wants to feed on the mortals of the various material planes. He/it is a patron to Warlocks ofr the most part.
Edit: apparently the Neogi (form Volo's Guide to Monsters) are particularly adept at contact hi/it and getting power.
Hadar, The Dark Hunger, The Craven Star. It is to my knowledge that Hadar is star that was corrupted by the influence of ancient aboleth lords. This caused it to form an ego, and either in an attempt to avert it's own destruction or to spread entropic nothingness, they seek to consume all that there is. Thus, spells that sport the name Hadar are often ones that try to bring a modicum of the entity to the caster's location so that it may render what crosses paths with it to ruin. The D&D 5e stream, High Rollers, had taken the concept of Hadar and merged it with that of an nigh unstoppable black hole, their similarities are notable after all.
I'm just going drop this link, because the others haven't yet.
https://forgottenrealms.fandom.com/wiki/Hadar
Please check out my homebrew, I would appreciate feedback:
Spells, Monsters, Subclasses, Races, Arcknight Class, Occultist Class, World, Enigmatic Esoterica forms