The Thunder Crown is a Crown-class head armor found in Golden Sun. It is found in a chest in the later portion of Venus Lighthouse. As a Crown, it can be equipped by all Adepts. Its buy value is 7500 coins and its sell value is 5625.

The Thunder Crown increases the wearer's base defense by 40, and it increases PP regeneration by 4. However, it is an item that has an equipment curse.

This is very likely the best piece of headwear for whichever Adept of the party of the original Golden Sun is equipped with the Cleric's Ring to negate the negative effects of equipment curses, providing the highest Defense rating of all headwear in the first game and a useful PP regeneration bonus. If present on the original party when they join Felix's party late in The Lost Age, however, it becomes instantly outclassed, specifically by the Crown of Glory which you can win multiples of with Lucky Medals; a Crown of Glory is exactly like a Thunder Crown, but without the equipment curse and with twice as much PP recovery.

Basic Headgear in Golden Sun
Leather CapWooden CapMail CapNinja HoodLure CapJeweled CrownProphet's HatLucky CapThunder Crown
Basic Headgear in Golden Sun: The Lost Age
Leather CapWooden CapNurse's CapMail CapThorn CrownOtafuku MaskJeweled CrownProphet's HatFloating HatHiotoko MaskCrown of GloryAlastor's Hood

Basic Headgear in Golden Sun: Dark Dawn

Leather CapWooden CapNurse's CapMail CapLure CapJeweled CrownProphet's HatLucky CapUmbra CowlThunder CrownAlastor's Hood