From the Super Mario Wiki
The Quirks are an alien species originating from The Super Mario Bros. Super Show!. Quirks are humanoid in appearance and have light-green skin; they also have two trumpet-like noses jutting from their faces. The Quirks are the only known, native inhabitants of the planet Quirk.
The Super Mario Bros. Super Show! episode "Stars in Their Eyes", it is revealed that the Quirks had been enslaved by the evil Moon Man Koopa, Astro Mouser and their Koopa Troopa minions; the Quirks were forced to mine the rocks of Quirk and transport them to Moon Man Koopa's Quirk Factory.
After a lot of hard work, Mario, Luigi, Toad and Princess Toadstool managed to repair their spaceship with help from the Quirks and battle Moon Man Koopa in his spaceship. After a long and narrow battle, Mario, Luigi, Toad and Princess Toadstool managed to beat Moon Man Koopa, who next tried to land back on the planet Quirk.
Unfortunately for Moon Man Koopa, the Quirks, having been inspired by Mario, Luigi, Toad and Princess Toadstool, rebelled against Moon Man Koopa and hummed a song loud enough through their noses to cause Moon Man Koopa's Spaceship to malfunction internally. The Quirks, free from Moon Man Koopa's and his henchmen's rule, were last seen waving goodbye to Mario, Luigi, Toad and Princess Toadstool as they zoomed away in their spaceship.
It is possible the Quirks had some sort of interconnected mind system, as they are shown to speak in complete and perfect unison on several occasions.