Velstadt, the Royal Aegis

Velstadt's attack range is wide, making it a challenge for melee characters to safely land hits without the risk of getting hit by his massive weapon. Having a good shield with 100% damage reduction and high stability is a plus here, since you'll be able to protect yourself as you circle around him. Like the other bosses, Velstadt will tend to jump away when you're about to hit him so using slow but powerful weapons will require proper timing to connect. Staying close to him then evading at the last moment his attack lands is a good way to counterattack.

Ranged characters can take advantage of Agdayne's assistance. He's a great tank and will be able to withstand a lot of Velstadt's attack before getting vanquished. While Agdayne's keeping the heat from you, you should use your most powerful ranged attacks.

Otherwise, ranged characters with fast attack speed can land hits in between the boss' combos. If you don't have Agdayne with you, you'll need to time your attacks since he can easily catch you off guard when you're in the middle of casting. Once the boss is down to 50% HP, he will start using hexes. Ranged characters can take advantage of this while he's casting while melee characters must take care not to get too damaged by the boss' AoE.

Continue downstairs and ignore the prowling giant with the sword. Loot the King's Ring from the corpse. You can equip this ring and use it to open the large black doors that require the Symbol of the King to be opened. The Herald will appear from the stairs. Talk to her then return to the next bonfire.