The first ruler of unified England was King Æthelstan, who reigned from 924 to 939 AD. Æthelstan is regarded as the first King of the English after successfully consolidating various kingdoms, including Wessex, Mercia, and Northumbria. His reign marked a pivotal moment in English history as he established legal reforms, emphasized Christianity, and fostered trade and cultural growth. Æthelstan's accomplishments laid the groundwork for a more centralized English monarchy, unifying the diverse groups within the territory and setting the stage for future developments in the English nation.