From Destinypedia, the Destiny wiki
During their career, Satomi hunted down shadowed killers in Murder Row, which resulted in hundreds of deaths for the Guardian. Satomi then researched the experiments in thanatonautics carried out by Osiris and Toland, the Shattered before undergoing their own death research. After discovering that Void energy lingers after all deaths, Satomi created the Mask of the Quiet One in order to allow Titans to heal themselves and use their abilities faster when being hurt or using the Void to kill their enemies. Their work was deemed dark by Satomi's fellow Guardians, and Satomi defended the Mask's abilities, and its horns, by accusing the other Guardians of being too dark themselves by ignoring how they had learned to recycle Void energy and return it to the Light for their benefit.