In the original Donkey Kong, the character who later became Mario was called Jumpman.
Donkey Kong debuted in arcades in 1981, years before Nintendo consistently used the name Mario. Players controlled a carpenter who climbed platforms and ladders, jumped over barrels, and tried to rescue Pauline from the giant ape Donkey Kong. Promotional material and documentation referred to the hero as Jumpman.
The name Mario emerged during the game’s American rollout. Nintendo of America staff reportedly chose it after Mario Segale, the landlord of the company’s warehouse near Seattle. The new name gradually replaced Jumpman, and Mario later became Nintendo’s most recognizable character. The original game’s hero was therefore Mario in retrospect, but Jumpman is the canonical name associated with his first Donkey Kong role.
Mr. Video is a related but different early label: Shigeru Miyamoto had used that name when imagining the character before Donkey Kong. Luigi was introduced later, in Mario Bros. in 1983. That is why neither Luigi nor Mr. Video is the best answer for the character’s name in the original arcade game.