Quick lore question?

[NecroDancer]

Looking at the warlock spell list I was just wondering who are Agathys and Hadar? My guess would be that they are Eldritch pact master but is there any actual lore on them?

[Tanarii]

Agathys is the innermost layer of Carceria, the Neutral Evil outer plane (leaning towards Chaos). It's also known as the Prison Plane.

Edit: I went looking for Hadar online, but all I could find in a few minutes of looking was:
"Hadar: Hadar is the extinguished cinder of a star lurking within the cloaking nebula of Ihbar"
http://www.wizards.com/files/366_Warlocks.pdf

[NecroDancer]

Thanks, this will be very useful!