Marthese was a housekeeper working for Mastermind when he first arrived on Malta and she became his obsession, soon disappearing from the public and severing any contact with her family and friends.  Mastermind refashioned her as a blue-skinned aquatic humanoid with incredible physical features.  She evidently had very little family anyway so her absence was met with gossip and innuendo, but little actual investigation.

She rarely ventures into the towns of Malta, preferring to live beneath the hard rock within Mastermind's headquarters.  She has been seen frequently with Mastermind in other places, however, which may indicate that she feels sensitive about her appearance when visiting the places of her youth.  Or it may not indicate that.  Since her transformation Manta has shown a diminishing connection with her humanity.

Manta is always by Mastermind's side, although her overt attractiveness and crude sexuality disturb him and she often finds herself alone.  She has adapted to her new life and spends most of her time away from Mastermind exploring her new form which generally means hunting beneath the waves of the Mediterranean Sea.

Manta is both passive and difficult to anticipate as she continues to move away from her former 'human' life.  She considers herself a unique creature and has this idea reinforced to her by Mastermind frequently.  She enjoys her physical prowess and ability to dominate the world beneath the waves.  Her mannerisms around other people are quite unpredictable and usually involve some kind of social faux pas.

She is considered weird and a little scary by those who know her (even Mastermind is sometimes surprised by her behaviour or lack of understanding in social situations).  Her speech patterns have also altered, particularly the 's' sound and her tendency to roll words together.

She has a killer instinct and is a predator.  This is becoming clearer as the years pass, although Mastermind is satisfied with the development and utilises her talents to his advantage.

"Ahhyess, the fish turns to flee... but it is too lateyesss."

Manta has been genetically engineered by Mastermind and has an amphibious physiology as well as enhanced physical attributes.  Her normal strength range allows her to lift in excess of 6000kg, but when immersed in water her strength increases exponentially allowing her, at her peak, to lift in excess of 75 tons.  She has incredibly quick reaction times as well as enhanced agility and is able to fly at great speeds above and below the water.

Her physical appearance is striking.  She has blue skin which is hardened to provide protection from the dangers of the deep, as well as glowing yellow eyes which allow her to see into the infrared spectrum as well as providing her with night vision capabilities.  Her ears are small and pointed and she is able to hear ultrasonic vibrations, and while under water she is able to emit sound waves to provide her with limited sonar capabilities.

Manta wears a flowing cape which is stitched with a kevlar weave and protects her from serious harm.

When people look at Manta they inevitably feel a sense of unease.  She has an alien presence with a predator's stance.  She watches people like they might be good hunting and always weighs up a person's worth first as potential prey and then as perhaps something more useful.  The Mastermind's genetic manipulations have endowed her with blue skin, yellow eyes, pointed ears, gills at her neck and an unearthly grace.

Manta wears a silver-grey cloak, lined in dark purple, over a white bikini.  She is never seen in anything else.

Before her transformation she was a plain Maltese girl, but she remembers very little about that life and doesn't seem overly curious about finding out more.