An administrator (one who administers affairs).
A systems administrator (one who maintains a computer system or network).
A user of a discussion forum, website, etc. with privileges allowing them to control or restrict the activity of other users.
Administration, or administrative work.
An administration (a body that administers; the executive part of government).
To serve as an administrator for or of.
A person assigned to manage a client's affairs.
In intelligence organisations, a person who manages a network of agents.