Double

Double (JP: ダブル) is a monstrous, transforming creature working under the Trinity, responsible for ensuring that the Skull Heart falls into the "right" hands and manipulating events according to the goddesses' will. Her current guise is as a nun under the name Sister Agatha and Main Antagonist of Skullgirls.Double is one of the playable characters in Skullgirls. Her homestage is the Grand Cathedral, but Gehennais also referred to her "domain" and is even suggested to be an extension of herself.

Despite MikeZ stating that Double was female, her gender is still listed as Unknown on the official site.

The nun form that she takes is based on no one in particular; it's just a form she takes to blend in at the cathedral.

Double is speculated to have been created by the Trinity as she shares a few physical traits from each member.

Venus views Double as a maid or a butler, although it’s not quite as straightforward as Double represents many things.

Personality
Double is an enigmatic character who lacks a distinct motive or will that most of the cast have and rarely emotes. She mostly maintains a stoic demeanor when conversing with someone. However, she has shown bouts of pure rage and hatred when it comes to characters like Squigly (Squigly refuses to obey Marie's orders) and Eliza (Eliza killed Aeon and Venus). Double's encounter with Eliza implies that she has an unspecified connection to Queen Lamia, such as being her avatar or 'shadow'. She has been shown to be a manipulative figure who will do anything to further her agenda and create Skullgirls. Even if she follows their orders, Double will not hesitate to eliminate a Skullgirl should they put The Trinity's plans to a standstill.

Backstory
Though her origins are vague, Double is devoutly loyal to the Trinity, using her shape-shifting powers to support the Trinity's ominous agenda. As such, she is an ally of the Skullgirl, and appears to take steps to ensure the creation of new Skullgirls. Double is capable of transforming her nightmarish form into that of any person, but she often takes on the appearance of a smiling nun. Double can frequently be found in the Grand Cathedral of the Divine Trinity, listening to confessions and tending to the catacombs beneath.

Fourteen years before the events of the game, Double attended the birthday of Selene Contiello in the disguise of a beautiful socialite, giving her the Skull Heart. She then notified the Medici Mafia that Squigly's family, the Contiellos, possessed the dangerous artifact, undoing decades of accumulated good-will in an instant. As Double expected, the Medici's gunned down the entirety of the Contiello family, thereby sending a message to the rest of the world that they were not to be challenged.

By the time of the game itself, Double is working under the newest Skullgirl Marie, serving as one of her two attendants (alongside Valentine). In her story mode, it is revealed that she is responsible for Marie's transformation, taking in the girl when she fled from Rommelgrad and offering her the Skull Heart as a way to fulfill her desires. However, Marie's strong will allowed her to fight against the Skull Heart's influence, delaying the Trinity's plans. Learning of her masters' displeasure, Double began searching for possible replacements for the disobedient Marie.