Mario

Mario is the main character on The Paper Mario Super Show. He is appears in the following episodes:

Vivian joins the adventures (show debut)

Vivian's Restaurant

Bowser is back

Kooper vs Black Ninjakoopa

Fransisco From Far Away

The Koopalings Bodacious Return

Midbus Returns

F.U.F.F. is Born (mentioned)

The Quest for the Fire Stone

Weegee's Revenge

The Monster under Toad Town

The Paper Mario Super Show Movie part 1

The Paper Mario Super Show Movie part 2

Positions on the show
Leader of the Mushroom Pack

Behavior to his party members
Mario is very nice to his party members, and agrees to go on quests with them to get them something (for example, Mario agreed to go on a quest to the Pokemon World with Vivian, Kooper and Toadsworth in the episode The Quest for the Fire Stone).

Relations with other characters
Luigi

Luigi is Mario's little brother, so Mario and Luigi are in good terms with each other.

Peach

Mario and Peach are in good terms with each other (and they also have a crush on each other) since Super Mario Bros, and also have a great friendship.

Bowser

Bowser is Mario's archnemesis, so they share bad chemistry.

Mushroom Pack

Mario shares good chemistry with his party members, (which is stated above) and even allows them to live at his house. He often sends his party members to Bowser's Castle to inquire information on Bowser's next scheme.

Trivia
Mario has so far appeared in every episode of the show, except F.U.F.F. is Born, but he is mentioned by Fransisco in this episode.

Mario is one of the three characters to swear, the second being Vivian and the third being Leopold.