Magister is the eighth grade of the Societas Rosicruciana in Anglia, opening its Third Order alongside the ninth and final grade, Magus. Advancement within the Third Order is the sole responsibility of the society's Supreme Magus, the head of the order, unlike the First and Second Order grades administered by local Colleges and regional Provinces respectively. That concentration of authority at the top of the sequence marks the Third Order, Grades VIII and IX, as the society's most restricted tier.
The SRIA's nine grade structure, founded in 1866 and 1867, predates the Hermetic Order of the Golden Dawn by roughly two decades, and it was this structure, Third Order included, that supplied the template the Golden Dawn's founders adapted for their own order, though the Golden Dawn's later Third Order, Magister Templi, Magus and Ipsissimus, framed its highest grades around the Secret Chiefs rather than around a single administering officer the way the SRIA's Supreme Magus does.
Because advancement to this level rests with one officer rather than a body of officers, the SRIA's Third Order is documented in Masonic reference literature as considerably smaller in practice than the First and Second, a pattern of a broad base narrowing sharply toward the top that the Golden Dawn's own later three tier structure echoes without exactly reproducing.