I can provide a bit of context here.
I originally got the name Obox-ob from the list of other demon lords that was printed on page 35 of the 1st edition Monster Manual II. For whatever reason, the sound of the name really appealed to me, and I ended up using it as the name of the primary bad guy deity for my homebrew setting, back in the late 80s. His footprint in my homebrew continued to grow as I played multiple campaigns, and a particularly memorable and long-running campaign I ran in college in 1991 and 1992 was focused on his attempt to absorb the planet my homebrew was set on into the Abyss as sacrificial fuel to cement his position as the ruler of the 666th layer of the Abyss. Fortunately, the PCs managed to defeat him... (well, most of them did–one of the PCs ended up switching sides and became one of Obox-ob's minions, which was kind of a surprise to all of us!).
Anyway, fast-forward a decade or so. I'd been hired to help write Fiendish Codex, and one of the things I wanted to do was explore the idea of "proto demons"—whatever came BEFORE demon kind in the Abyss. I made up the obyriths to fill this role, and set up Obox-ob as the most powerful of their kind, presenting him as the obyrith version of the demon's Demogorgon. In creating his lore for Fiendish Codex (and the role he played in the Savage Tide adventure path for Dungeon Magazine), I drew from that campaign I ran back in college. It made sense to me to give a little back, since I'd originally gotten the name from D&D (as far as I know, there is no real-world mythological Obox-ob, but if someone has information otherwise I would LOVE to hear it!), and so a fair amount of the homebrew version of him ended up infusing the D&D version.
The little bit about how he "almost managed to draw an entire world into the Abyss..." is, I suppose, an easter egg for me, since it's a nod to the plotline of that campaign I ran back in college. It's fun flavor for him, I think, but I kept it relatively world-neutral and vague so any GM could end up expanding on it as she saw fit, or so that future authors for D&D products working for WotC could run with that thread and expand on it however they wished.
As an amusing little side note, when I transplanted a large number of my homebrew deities over to serve in Pathfinder's campaign setting, I took another of my homebrew deities, Rovagug, and pretty much smooshed a LOT of my unused-for-D&D Obox-ob lore into him. So if you want to see how I would have continued to develop Obox-ob in D&D in a parallel world where I continued to expand things there, just look to Rovagug in Pathifnder's lore. I do kinda miss not being able to have Obox-ob play that role for Pathinfder, but since the name itself is, as far as I know, something that Gygax invented for the Monster Manual II back in the early 80s, I think it's only right that Obox-ob stayed a D&D monster in the end.
NOTE: I've not been involved in expanding Obox-ob further in 4th or 5th edition D&D, and so don't have any insights into what he's been up to since then. But as the one who took Gygax's name-drop in the MM2 back in the day and gave him a larger role in the game, felt like a good place to pop in and drop a wall of text!
