From Lexicanum

The Master of the Administratum is the title of the head of the Administratum. The holder of the rank also holds a position on the High Lords of Terra. Among the High Lords this rank is the most powerful. Accordingly, the holder of this rank is probably the single most politically powerful and influential man in the galaxy.

The title, however, is purely nominal. As a High Lord, he has no time to devote to the Administratum, and no duties beyond the occasional ceremonial appearance.

Sources

• Codex Imperialis (1993), by Rick Priestley, pp. 14,48