Creature that gains HD by eating other creatures?

[Matrota]

In 3.5e, I seem to recall reading somewhere about a creature that didn't gain xp, but instead gained levels by eating other creatures. I believe the HD gain was based on either the consumed creatures HD or its size category. I recall there was a cap, and assume it was some sort of monster that could only progress to a certain point. Does anyone know the creature I'm talking about?

[Vhaidara]

barghests are the major one, though i believe there's also a giant type (dusk?) that does the same

[Mike Miller]

Maybe Devourer? I forget. I feel like an epic monster does it too

[Shadowquad]

I think the creature you're thinking about is the Redcap, an Evil Fey from MMIII. It doesn't quite eat its victims, but rather soak its cap into their blood, thus gaining HDs, up to 20.

As others have said, other creatures such as the Barghest and the Dusk Giant indeed consume their victims and gain HD

[ShurikVch]

Also, Maurezhi and Juvenile Nabassu demons (from Fiend Folio and Fiendish Codex 1)

[exelsisxax]

Barghest is the one you're thinking of, but as also mentioned above there are some others with similar capabilities.

[Thurbane]

barghests are the major one, though i believe there's also a giant type (dusk?) that does the same

Dusk Giant (Heroes of Horror, p. 147).

[daremetoidareyo]

Beast of xvim from monsters of faerun.

Touch of hate feat PGTF will allow you to make them but they are instead called beasts of bane. Cleric 9 with aspect of the wolf as an extra spell (complete arcane) who has this feat can become one themselves.

[frogglesmash]

The Ulgurstasta from Fiend Folio creates skeletons by swallowing living creatures, and gains 1 point int for every 1,000 skellies it creates. Not exactly what you're looking for, but it's similar.

[ksbsnowowl]

I think they've all been touched upon, aside from the reprinting of the Beast of Xvim template, but to consolidate them into one post:

Barghest (MM1)
Beast of Bane [updated Beast of Xvim template](Shadowdale - The Scouring of the Land)
Beast of Xvim template (Monsters of Faerun)
Dusk Giant (Heroes of Horror)
Maurezhi demon (Fiend Folio)
Nabassu (Juvenile) demon (Fiendish Codex I) - This one doesn't actually gain HD, just bonuses that approximate it, and then it hits a limit & transforms into a Mature version that has 10 more HD.
Red Caps (MM3)

On a tangential note, Bheur Hags from Unapproachable East can eat foes, and like a foe that was eaten by a Barghest or a Beast of Xvim, the victim can only be brought back by a Wish or Miracle, and even that is only 50% likely to work. The Bheur Hag does not advance from this activity, though.