Considering the serious storyline of the DBZ, he serves as the comic  relief.

When Cell called for the best warriors in the world  to challenge him in the Cell Game, Mr. Satan, the world boxing  champion answered the challenge and declared himself the savior of  the world.

He regarded the powers of Cell and the Dragon Ball  Warriors as mere "illusions." Even when the whole world shook in the  epic battle between Son Gohan and Cell, he stood firm to his view.  However, even though he did not outwardly admit what he saw was very  real, his cowardly excuses to avoid battle and taking the credit for  defeating Cell readily demonstrated otherwise.

Mr. Satan  fooled the whole world of his powers and continued to do so when he  paid off #18 for his title in the Budokai after Cell was  defeated.

The most interesting portion of his presence in DBZ  was his friendship with Dämon Boo. Like no one else, he brought out  the "good" in Boo and even convinced Boo not to kill  anymore.

Despite of his lies, Mr. Satan did contribute to his  share to saving the earth. In the Cell Game, it was him who brought  what was left of #16 to Son Gohan, who ultimately drove Gohan's  spirit to transform into Super Gohan.

He also contributed to  the defeat of Majin Buu by convincing everyone to contribute their  share of energy to Son Goku's Kenki Dama which ultimately destroyed  Boo.