Ostiarios (Greek: ὀστιάριος, from the Latin ostiarius, "doorkeeper, usher") was a Byzantine court dignity reserved for eunuch palace officials.
[1][2] As a pure dignity, to be held alongside proper offices, the ostiarios is first recorded in historical sources for the year 787.
By this time, the title seems to have become firmly established as a dignity, although there is still mention of it being an active function, such as in Philotheos's Kletorologion of 899 of an "imperial ostiarios" performing the duties of an usher.
[3] The dignity was an awarded title (διὰ βραβείου ἀξία, dia brabeiou axia), with a gold band with a jewelled handle as its characteristic insigne, whose award (βραβείον, brabeion) also conferred the dignity.
It was the fourth-lowest dignity for eunuchs, above the spatharokoubikoularios and below the primikerios, and was reserved specifically for them.