From the Super Mario Wiki
Muskular is one of the seven Star Spirits. As his name implies, Muskular is a very strong Star Spirit who likes to work out, first appearing in the original Paper Mario as the fourth Star Spirit to rescue from Bowser. He likes to wear a sailor's hat, meaning he could like the water or just chooses to wear the hat, and is always full of energy. He was guarded by General Guy and his troops in the Shy Guy's Toy Box.
In Mario Party 5, Muskular, along with all the other Star Spirits, returns. Here, he is the guide of the minigame mode.
Muskular appears as a sticker in Super Smash Bros. Brawl. It raises launch resistance by 13, and it can be used by any character.
Names in other languages
||From fortísimo (very strong) and estrella (star)
||From patate (potato) and étoile (star)
||From astro (star), and mare (sea), probably referring to his hat