Marrina is a member of the alien species the Plodex, which sends its eggs to various planets. When the eggs hatch, young Plodex take the forms of the native species they encounter. As an egg, Marrina landed in the Atlantic Ocean about 40,000 years ago, at the turn between the Middle Paleolithic and the Upper Paleolithic and remained dormant for thousands of years. This incubation place was responsible for her adaptations to aquatic environments. The egg was found by fisherman Tom Smallwood as he was drowning during a storm. It proved buoyant enough to bring him to the surface and thus save his life. Tom took it home to Newfoundland, Canada. The egg was opened prematurely by his wife Gladys Smallwood, causing Marrina to imprint a humanoid female form. The Smallwoods accepted her as their daughter. She leaves home at sixteen years of age to join Beta Flight, a team of superheroes trained and funded by the Canadian government. After performing well in Beta Flight, Marrina is promoted to Alpha Flight, although her field duties only begin after the team went freelance. She learns of her alien origin when captured by the Master of the World, and is rescued by Alpha Flight and Namor alongside the Invisible Woman. Following this she leaves Alpha Flight and stays with Namor. Marrina is captured by Attuma, and reverts to savagery for the third time but overcomes it. Marrina marries her lover, Namor. She serves alongside him on Avengers missions and receives honorary membership, and also serves as the queen of Deluvia.