The parakoimōmenos (Greek: παρακοιμώμενος, literally "the one who sleeps beside [the emperor's chamber]") was a Byzantine , usually reserved for eunuchs. The position's proximity to the emperors guaranteed its holders influence and power, and many of them, especially in the 9th and 10th centuries, functioned as the Byzantine Empire's chief ministers.
The title was used anachronistically by various Byzantine writers for prominent eunuch court officials all the way back to Euphratas under Constantine the Great (reigned 306–337), the notorious Chrysaphius under Theodosius II (r. 408–450), or an unnamed holder under Emperor Maurice (r. 582–602). However, it was most probably created only later in the 7th century, and is first attested securely only under Leo IV the Khazar (r. 775–780), when the chronicler Theophanes the Confessor records the existence of a "koubikoularios and parakoimomenos". In the beginning, it was a modest office, given to those koubikoularioi (from Latin cubicularius, denoting the eunuch servants of the emperor's "sacred bedchamber" or sacrum cubiculum) who were tasked with sleeping outside the emperor's chamber during the night as a security measure. As evidenced by seals from the 7th and 8th centuries, it was usually combined with other palace functions, such as the epi tēs trapezēs, and its holders held lowly dignities such as ostiarios. It is possible that in the cases where several co-emperors reigned at the same time, a parakoimōmenos would be assigned to each.
From the mid-9th century, however, the office grew in importance, outstripping its nominal superior, the praipositos, until it came to be regarded as the highest post reserved for eunuchs, with its holders raised to the dignity of patrikios. Over the next two centuries, many of its holders were able to use their proximity to the imperial person to exercise considerable political influence. Some of these men, exceptionally, were not eunuchs. During the reigns of weak or uninterested emperors, holders of the title parakoimōmenos, such as Samonas, Joseph Bringas and Basil Lekapenos, functioned as chief ministers, while Basil the Macedonian (r. 867–886) was able to use this position to eventually usurp the throne from Michael III (r. 842–867).