The thunder god in the first Mortal Kombat game is Raiden.
Raiden is one of the franchise’s oldest and most important characters. He is portrayed as the protector of Earthrealm and draws on powers associated with thunder, lightning, teleportation, and supernatural strength. In the original game, he is one of the playable fighters competing in the tournament on Shang Tsung’s island.
The character is commonly depicted wearing a conical hat and traditional-inspired clothing. Across different timelines, Raiden may act as a mentor, protector, or participant in events that determine the fate of the realms.
Fujin is also a god in Mortal Kombat, but he is associated with wind rather than thunder and was introduced later. Shinnok is an elder god and antagonist, while Shao Kahn is an Outworld emperor.