Little T.

From the Super Mario Wiki

The letter has a picture of Little T. on it.

Little T. is a Toad in Paper Mario who trains at the Dojo. As the name implies, he is a little Toad and also lives in Toad Town. He even acknowledges in his letter to Mario that he is just a little toad. He spends his time training at the Toad Town Dojo. Little T. is an amateur fighter, but he has a lot of spirit as he wants to save Princess Peach some day. He is one of the first characters in the game to send Mario a letter.

Major Toads
Toad \| Toadette \| Toadsworth \| Toad Brigade
Toad Species
Cave Mushrooms \| Dryites \| Fryguys \| Mermushrooms \| Mini Toads \| Toads
Minor Toads Battle T. \| Chancellor \| Chanterelle \| Doe T. \| Dr. Toad \| Excess Express Conductor \| Excess Express Engineer \| Fice T. \| Frost T. \| Game Boy Toad \| Gardener \| Gaz \| Ghost T. \| Gramma Red and Gramma Green \| Grandma Toadstool \| Harry T. \| Heff T. \| Herb T. \| Hinopio \| Hollijolli Mayor \| Jack \| Jolene \| Little T. \| Mailtoad \|Master Poet \| Minh T. \| Monstermama \| Mort T. \| Mr. E (MPA) \| Mr. E (PM) \| Mrs. Shroomlock \| Mushbert \| Mushroom Retainer \| Muss T. \| Niff T. \| Pine T. \| Pine T. Jr. \| Plenn T. \| Porter \| Prince Mush \| Professor Fungi \| Puff \| Radio Contest Toad \| Raini \| Raz \| Rose Town Innkeeper \| Russ T. \| Shroomlock \| Starshade Bros. \| Tayce T. \| The Master \| Thriff T. \| Toad Minister \| Toad Waitress \| Toad in the Desert \| Toadbert \| Toadia \| Toadiko \| Toadofsky \| Toadsworth the Younger \| Toce T. \| Toodles \| Vanna T. \| Vault Guard \| Zess T. \| Zip Toad
Toads in Other Media Bingo \| Chef Spore \| Down Under Land Mayor \| Emperor Ed \| George Washingtoad \| Gramps \| King Windbag's Servant \| Mayor Fettuccine \| Minister of Massage \| Moldy \| Mushroom Doctor \| Mushroom Nanny \| Mushroom Pilot \| Mushroom Referee \| Obi-Wan Toadi \| Pine \| Prince Hugo the Huge \| Pronto \| Scooter \| Sultan \| Swiss Cheese Alps Mayor \| The Mushroom Marauder and Jake "The Crusher" Fungi \| Toad's Cousin \| Toadster \| Wooster