Oliver is a Charlemagne kingdom prestige hero and requires 70,000 prestige to unlock.
Unit Type - Swordsman: High Block Rate. Gambit - Entrench: Deal low gambit damage to a single target and enter a defensive stance, reducing all normal and gambit damage to 1 (2 if critical) until the next turn.
Initial status is 71 bravery, 75 tactics and 63 magic and has 390 units.
Oliver offers too little and comes too late. If you're intent on using an entrench hero then Oliver is the one to choose, otherwise don't consider him too much.