The Walker Boss is a mob that can be found at the top of a Walker Castle if not previously defeated.
It can teleport to the player, uses a shield to block attacks, and has a "gravity well" ability which pulls the player in a specific direction. It has 250 hitpoints and diamond armor.
It can easily knock the player off the tall castle causing large if not fatal amounts of fall damage; if the player survives the fall then the walker boss can teleport to them to finish them off. Feather falling enchantments on ones boots is recommended for this reason.
As hit points decrease on the boss its appearance changes so that its armor breaks until it is only wielding its sword and shield. It is also the only non-creative source of the Ender Sword, a rare and powerful sword. It also drops a Diamond Block upon death.