Alfonso is Mario and Luigi's younger brother and is Gustavo's older brother. Alfonso and Gustavo came to the Mushroom Kingdom to find their older brothers who have lived in the Mushroom Kingdom for a while. Alfonso looks similar to Mario, but thinner, wears orange, slightly taller, and has a slightly pointier mustache.
Alfonso is an all-in kind of guy, he willingly helps Mario and Luigi rescue Peach and goes on adventures with his bros. He never backs down from a challenge, and often is journeying through the Mushroom Kingdom. He was only 10 when Mario and Luigi went missing after a plumbing job in Brooklyn, and does not want them to go missing again. Alfonso is a very brave person, proving his bravery to be greater than his brother Mario at times.