Stu Fletcher is a character in Visiting Aunt Miriam, he is the father of Mario and Luigi Fletcher, husband of Diana "Didi" Fletcher and the son of Louis Fletcher and his wife Erica Fletcher.
Stu was born in Kanto to Louis Kalhern Fletcher II and Erica Agatha Fletcher (née Potter), Stu met Diana while traveling in her native region, which is "somewhere near the Kalos region" (the region is based off of Italy). Stu and Diana got married and had two sons, Mario Fletcher and Luigi Fletcher. Mario was named after Diana's father Mark (Mario is the Italian version of Mark) and Luigi was named after Stu's father, Louis (Luigi is the Italian version of Louis).
Not long after Mario and Luigi were born, Stu and Diana went missing, it was thought that Mario and Luigi had gone missing, but they were both safe and sound. The babies were quickly put into foster care, surprisingly, the foster parents had the same surname as Mario and Luigi did, which helped with any confusion.
Currently, Stu and Diana's whereabouts are still unknown, it is unknown if they are alive and well or dead.