Roswaal K Mathers (ロズワール・K・メイザース), formerly known as Karl (カール), was the son of Roswaal J Mathers, and the father of Roswaal L Mathers. He was possessed by Roswaal A Mathers some time after the untimely death of his mother.
As a child barely the age of 10, Roswaal K Mathers had a short statue, befitting of a child. His face was well proportioned and very handsome, according to Wilhelm. Just like his ancestors, Karl had shoulder-length indigo hair–very similarly to how Roswaal A Mathers can be seen during the Sanctuary flashback in Arc 4. On his handsome face, there was a pair of heterocromatic eyes–one blue and one yellow.
He speaks quite politely. Though he was usually cool and collected, there were moments where his childishness would show such as when he stamped his feet in frustration.
Karl was born out of wedlock as the son of Roswaal J Mathers. During the Demi-Human War, he remained at the Roswaal Mansion, and was raised by Clind. With Julia kept occupied by her role as the Royal Court Mage during the attacks on the Astrea Mansion, Clind continued to raise Karl. Following the unexpected death of his mother, Karl was possessed by the original Roswaal, and inherited the Roswaal estate, along with its assets.
- Karl created a theory that allows objects to be imbued with yang magic buffs.
- Starting with his original body, Roswaal has been changing his middle initial every time he possesses a new descendant. His original initial was A, making his current body his 11th one.
- All Roswaals middle names follow the English alphabet thematically.
- In Poltergeist Story, it is revealed that Roswaal K Mathers created a number of automated dolls, which guarded his mansion and attacked everyone who approached his home. Following Roswaal K Mathers' death, the dolls remained on active guard duty, until Roswaal L Mathers deactivated them.