Real name: Sarah
Other aliases: None
Identity: The general populace of Earth is unaware of Marrow's existence.
Occupation: (current) Member of the X-Men, (former) Member of the Morlocks, leader of Gene Nation
Legal status: Presumed citizen of the United States with no known criminal record.
Place of birth: An undisclosed location in the United States
Marital status: Single
Known relatives: None
Base of operations: Mobile
Group affiliation: (current) X-Men, (former) Morlocks, Gene Nation
First appearance: UNCANNY X-MEN #325

History: Marrow is a mutant who, due to the physical appearance of her mutant abilities, hid herself as a young girl in the sewers underneath New York City as a member of the Morlocks, a group of mutants who were also physically deformed.

Marrow managed to survive the Morlock massacre by the Marauders and was later taken, as a young girl, to another dimension by the mutant Mikhail Rasputin in order to survive the destruction of the Morlock Tunnels.

Time passed quicker in the other dimension, and Marrow returned a few years later as a full-grown adult leading Gene Nation, a rebel faction of Morlocks who wanted revenge for the massacre. Marrow and Gene Nation kidnapped a subway car loaded with humans on the anniversary of the massacre, in order to kill a human for every Morlock that died that day. The humans were rescued, and Marrow battled the X-Man Storm. Marrow had attached the triggering device for a bomb to her heart, telling Storm that the only way to stop the bomb was to stop her heart. Storm, needing to end the battle, ripped Marrow's heart out of her chest.

It was later discovered that Marrow survived the fight, as her mutant physiology had granted her a second heart. Marrow later resurfaced in New York in order to stop the Prime Sentinels of Operation Zero Tolerance. Marrow encountered the X-Man Iceman and the mutant Dr. Cecilia Reyes, and subsequently became a member of the X-Men.

Height: 6 ft.
Weight: Unrevealed
Eyes: Pale Blue
Hair: Purple

Strength level: Marrow possesses the normal human strength of a woman her age, height, and build who engages in intensive regular exercise.

Known superhuman powers: Marrow is a mutant whose physiology has radically altered from the human norm. She had at one time possessed two hearts; the second continued functioning when the first was removed.

Many of Marrow's bones grow to an abnormally large size and protrude from her skin without causing any physical damage to herself. These bones are normally blade-shaped, and Marrow is proficient at using these blades as throwing weapons or in hand to hand combat. Once Marrow has removed any of these bones new bones grow in their place at an unspecified rapid rate. Marrow's entire skeleton has enhanced durability, giving her some degree of physical protection against concussive impact.