From the Super Mario Wiki
The Master is a powerful martial artist and the resident teacher of the Toad Town Dojo. He is a Toad who appears in the game Paper Mario. If Mario defeats his students Lee and Chan, the hero will have the opportunity to challenge the Master himself in battle. In fact, Mario can fight the Master three times, and can earn (in order) the Third Degree, Fourth Degree, and Diploma cards. However, each time Mario wins a battle, the next fight with the Master will become exponentially harder. The Master's appearance in the third battle is the same, except he is surrounded by a golden aura. With experience and skill (and maybe a few tricks), Mario can defeat the Master's third and most powerful form and earn the Diploma. It is highly recommended that Mario has equipped Zap Tap Badge or uses Volt Shrooms to electrify himself. This prevents The Master from using his Dashing Uppercut and Dashing Kicking Uppercut attacks that cause massive damage to Mario.
In his final form, the Master is actually stronger than the final boss, Bowser (in his powered-up state); while both have 99 HP, The Master has more powerful attacks than Bowser. Much like Bonetail in the sequel, the Master is the strongest opponent in the game and is completely optional, thus he is the game's superboss.
The Master is also similar in many ways to the character Jinx from Super Mario RPG: Legend of the Seven Stars. Both Jinx and the Master are expert martial artists who train disciples in schools. Additionally, Mario has to fight both Jinx and the Master three times each, with every battle getting progressively harder in each case.
Paper Mario Stats and Tattle Information
Max HP: 50
Moves: Punch (6)
Max HP: 75
Moves: Punch (8), Dashing Uppercut (5, then 6)
Max HP: 99
Moves: Punch (10), Dashing Uppercut (6, then 7), Dashing Kicking Uppercut (5, 6, then 7)
Names in other languages