Mario is the protagonist of Nintendo's Super Mario series. He is a prominent character in various movies and games on Newgrounds, especially in sprite based work. He is often portrayed in a humorous manner, either as a parody of his games or simply because of the popularity of his character. However, he is also the hero in many submissions, including the highly popular Super Mario Bros. Z series. Another fairly popular one being Bowser's Kingdom which was made by the creator of Smash Kingdom, another popular sprite series featuring Mario as one of the main characters.
One common theme of Mario submissions on Newgrounds is that they are often far more violent than the Nintendo games are. Unlike Mario games, where characters disappear upon being defeated, many Mario Flash often make abundant use of blood.
In total, searching for Mario in the Flash Portal will lead to over 2,000 results. Many Mario-based movies and games have been critically successful. The Mario collection on Newgrounds alone is four pages long, at least eight Mario-related submissions have won the Weekly Users' Choice Award, and at least seven have won the Review Crew Pick.