it is not a secret but very unexpected. when I heard of donkey kong, it was in context of donkey kong franchise which obviously feature Donkey Kong as main character just like mario is main character of mario games.
so technically first Donkey Kong game in Donkey Kong series is actually a Mario game. i understand why and how it happened. but this is a trivia that you either know or you would not believe from untrusted sources
Donkey Kong is the main character. Mario was just who the player controlled, he was so unimportant he didn't have a name and they just called him Jump Man.
It’s more the other way around: the first Mario game was a Donkey Kong game.
The user avatar is only “Mario” in appearance. He was called “Jump Man” in that game and even his outfit colours differed from the Mario games that followed.
you have it backwards . the game was "a Mario game", but it was called "Donkey Kong", so it comes under Donkey Kong franchise.
I don't know why we are making this arbitrary distinction between Mario games and Donkey Kong games.
But if we are the main Mario franchise games are the "Super Mario" games. Donkey Kong is not part of the "Super Mario" series and his "Mario" is not "Super" .
Worth remembering Mario Bros (Not Super)... it's basically the combat mode in SM3+ but as a stand alone game.