Loremaster is a core Prestige Class in 3rd Edition Dungeons and Dragons and Pathfinder. It's easy to qualify for and has solid enough class features for a Wizard, but lacks anything truely special and it's never seen outside of core only games, while in Pathfinder it didn't even get that due to Wizards having actual class features worth keeping. At the very end of Pathfinder's life this changed, as Loremaster got exclusive access to the feat Secret of Magical Discipline. This feat let anyone with a level in Loremaster cast any spell (regardless of class list, opposition school, ect.) once per day at the low cost of a feat, spell slot of the right level, and taking a full round action minimum. The feat can even be taken multiple times to gain extra uses. This is the kind of versatility that makes a class Tier 0.
An Archetype any class can take. You become a know it all that knows all the lore, Even things you shouldn't if the DM was foolish enough to let you roll.
Other feats including some cantrip, Read anything, and speed read.