The Kingdom of Essex is also not well documented. It produced relatively few Anglo-Saxon charters and no version of the Anglo-Saxon Chronicle. As a result, the kingdom is also regarded as comparatively obscure. For most of the kingdom’s existence, the Essex king was subservient to an overlord – variously the kings of Kent, Anglia or Mercia. Eventually the Kingdom of Essex became a principality of the Kingdom of Wessex, Which later became amalgamated into the other Anglo-Saxon kingdoms and henceforth became known as the Kingdom of England, ruled by a Wessex monarch.

Kingdom of Essex Monarchs
Reign: A.D
527 to 587
Æscwine (Aescwine) or Erkenswine, Erchenswine
According to the West-Saxon genealogy, Æscwine is said to be a decendent of Seaxnet, the legendary founder of the saxons, who was the son of the germanic god Wōden (Odin).
587 to 604
Some later sources suggest that Sledda is the founder of the East Saxon house.
c. 604 to c. 616
Sæberht (Saebert)
Later medieval legend claimed that Sæberht and his wife had founded the orginal abbey building at the site of the present Westminster Abbey, and that they had been burien in the church. First christian king of the East Saxons.
c. 616 to 617
Sexræd (Sexred)
Joint king with Saeward; killed in battle against the West Saxons (Wessex).
c. 616 to 617
Sæward (Saeward)
Joint king with Sexred; killed in battle against the West Saxons (Wessex).
617 to c. 653
Sigeberht the Little
Son of Sæward.
c. 653 to 660
Sigeberht the Good (Sigeberht II)
Murdered by his own kinsmen by two unnamed brothers; it’s believed to be Swithhelm and Swithfrith.
660 to 664
Believed to have murdered sigeberht II with his brother for being to friendly with Christians.
664 to 683
Joint king with Sebbi. Wulhere of Mercia established himself as overlord of Essex.
664 to c. 694
Sæbbi (Sebbi)
Joint king with Sighere; abdicated to enter a monastry, and succeeded by his sons Sigeheard and Swæfred.
c. 694 to c. 709
Joint king with his brother Swæfred.
c. 695 to c. 709
Swæfred (Swaefred)
Joint king with his brother Sigeheard.
Abdicated to take up life in a monastery in Rome, along with Cenred, King of Merica.
c. 709 to 746
Saelred (Swebert or Selered)
Probably joint-king with Swæfberht. Like his predeccessors, Saelred was not an independent ruler, but a dependent of the Kingdom of Mercia.
c. 715 to 738
Swæfberht (Swaefbert)
Probably joint-king with Saelred.
746 to 758
Swithred (also known as Swaefred)
Second son of Sæbbi. Like his predeccessors, he was a dependent of the Kingdom of Mercia.
758 to 798
Son of Saelred. Abdicated, where he made a pilgrimage to Rome and entered a Monastery.
798 to 825
Son of Sigeric. In 812 Sigered was reduced to duke by his Mercian overlords. In 825 he finally ceded his kingdom to Egbert of Wessex.
c. 825
Mercia defeated by Egbert of Wessex, sub-kingdom of Essex subsumed into Wessex