My ultimate ringhero would would be Celebrimbor for Imladris if it has to be a lore specific ring hero his powers would be:
Power 1: Switch weapon, he will switch between his sword and bow how ever his arrows would fire two at a time.
Power 2: Power of the the silver hand, Celebrimbor would turn all enemies in the area onto his side and they would gain more health and deal more damage.
Power 3: shadow kill, he will teleport into an enemy and deal heavy damage and if its a group of units he will kill teleport between each unit killing them until the whole unit is dead
Power 4: wraith blast a huge AOE similiar to word of power but it leaves a circle of blue fire once its been used
Power 5: Smith of eregion he upgrades all his fellow units with weapons made by him so all units deal extra damage and are also armoured with silver armor that gives them more defense.
However if the hero didnt have to be lore related it would be Artorias the Abysswalker from the series dark souls because he is the biggest badass ever.
Power 1: would be a passive called friend of the wolf: he would constantly be followed by his friend Sif the grey wolf and this passive also makes all beasts deal 50% more damage and have 50% more armour.
Power 2: Abysswalker: Artorias would power up with the dark energy of the abyss and launch foul curses around him damaging and posioning all nearby enemies he would also have 50% more armour while this power is active.
Power 3: Greatsword: Artorias would deal 30% more damage he would also be able to launch up into the air and slam down creating a mini AOE when he lands similar to earthquake
Power 4: Lunge: Artorias would fly across the ground into a horde of enemies knocking back all and dealing heavy damage he would then launch out an AOE of abyssal energy around him when he reaches the enemy target.
Power 5: Spinning slash: Artorias quickly spins, completing a full rotation twice. It has the potential to connect into an enemy twice deal knockback and very heavy damage.
Also he would be about the same size of Sauron and each of his attacks would be similar to Sauron's as in they will be AOE and also able to launch units into the air.