The King is a friend card used solely by Riku in Kingdom Hearts: Chain of Memories.
This card will summon King Mickey, healing Riku a little bit, stunning and hurting all enemies for a short time, and restocking Riku's deck. Stocking these cards will allow you to use the only sleight you can as regular Riku, MM Miracle. It increases the amount you are healed and the damage done to the enemies.