Corporal Pig (also known as Helmet Pig or Armor Pig) is a Medium Pig who serves as the second-in-command of King Pig's army and the secondary antagonist of Rovio's Angry Birds. He wears a stone (or maybe steel in the new design) helmet for a stronger defense. He is the third strongest pig variety in the game and serves as the chief enemy in the first set of levels in each theme. He also serves as a protector to King Pig. Corporal Pig is very much alike to Foreman Pig in-game ways, not actual looks but in strength. He serves as bosses: Herr Helmet (Poached Eggs), Hovering Helmet (Danger Above), Hardhat Hidalgo (The Big Setup), Billy the Pig (Ham 'Em High) and Cave Explorer (Mine and Dine). Corporal Pig first appeared in Poached Eggs Theme 1-21.

More facts here: https://angrybirds.fandom.com/wiki/Corporal_Pig