Harrold is the target practice dummy found in Squire's Knoll (Level 1). You can attack Harrold to test how much damage you can currently deal.
Upon destroying Harrold you receive various resources and two recipes. Notably Recipe for Football Goal and Recipe for Fluffy's Wits.
Harrold will re-spawn upon leaving and returning to the island.
Harrold has approximately 30,400 HP, so it is quite time consuming to destroy Harrold with early game weapons.