Larry Koopa is the first of Bowser's "children" in Super Mario Bros. 3, which is the first real Mario Bros game (Doki Doki Panic dressed as Super Mario Bros. 2 doesn't count) to feature bosses that weren't all Bowser impostors plus the real deal.
He's not too terribly difficult. In retrospect, kind of strange for them to give the first boss the power to shoot magic at you.
He's pretty easy, especially if you unleash a fury of fireballs at him.
And with his defeat, you can save the first king with the wand.