Eldritch scholar (3.5e Class)
From D&D Wiki
This is a variant warlock focused on invocation using instead of direct combat.
Lose: Eldritch scholar doesn't gain eldritch blast (if he uses eldritch essence invocations, they do their secondary effect, but no base damage), fiendish resilience and energy resistance.
Gain: Eldritch scholar gains one additional invocation each time he would gain odd-numbered eldritch blast dice (that means, level 1, 5, 9, 14, 20). In addition to it, when he gains access to a new grade of invocations, he can choose one sorcerer/wizard spell and add an invocation mimicing it to the invocation list of new grade. He can mimic spells up to 2nd level with least invocations, up to 5th level with lesser invocations, up to 8th level with greater invocations and up to 9th level with dark invocations.