The Powers of Matthew Star (1982)

Matthew Star was a prince on the planet Quadris, who was forced to flee to Earth when his planet's government was overthrown by despots. On Earth, he took the form of an ordinary high-school student (albeit one with superpowers), and was accompanied by his guardian Walt, who became the school's science teacher. The American government knew of Matthew and Walt's origin, and used them to act as agents on occasion.