Thunder, known in Japan as Ikazuchimaru(雷丸) is one of the four members of the Light Brigade led by Sarina. He and fellow member Frost were called upon by Sarina to battle Syrus Truesdale and Tyranno Hassleberry after they kidnapped Solomon Muto and baited them to the top of a large building in Domino City. Unlike Frost, he was more willing to use teamwork to win. He was given a copy of "Mirror of Duality" by Sarina, but could not use it since his Life Points were too low. However, Frost himself played the same card and won the Duel, with Thunder losing all his Life Points along with their opponents. He was sealed in a mirror by Sarina when she no longer had any use for him, but was freed alongside the other Light Brigade Duelists after Jaden Yuki and Aster Phoenix defeated her.
The "Ikazuchi" portion of his name in the Japanese version is derived from the word "ikazuchi" (雷), meaning "lightning".
Thunder travels through thunder, and seems to be in control of the "Zaborg the Thunder Monarch" spirit that presided over the city during his Tag-Team Duel.
Thunder plays a Thunder Deck, supported by Tag-Team Duel-exclusive cards. His tactics are less standard than his partner's in that he utilizes cards such as "Rampage Condenser" and "Lightning Talisman" to inflict damage through effects, rather than through battle. His primary card is "Zaborg the Thunder Monarch".