Aruego graduated from law school at the University of the Philippines and passed the bar.
[1] He lectured extensively at elementary schools, insisting on sketching a character into every book that he signed and teaching students to draw his alligators.
[1][2] Among his best known books were Whose Mouse Are You?, Leo the Late Bloomer[2] and Gregory the Terrible Eater.
He worked alongside Ariane Dewey in creating books that were about animals.
In 2006, they reunited to produce The Last Laugh, a picture book that had a strong anti-bullying message.