Keeper of Forbidden Lore( Fiendish Codex I: Hordes of the Abyss, p. 86)
A shred of demonic racial memory grants you knowledge of numerous ancient magical secrets.
You gain a bonus on Knowledge (the planes), Spellcraft, and bardic knowledge checks. The magnitude of this bonus equals the number of Abyssal heritor feats you possess. In addition, Knowledge (the planes) and Spellcraft are always class skills for you, and you can use them untrained.
You have trouble acquiring information in more conventional ways, which translates to a -2 penalty on Gather Information checks.