Aethelred II, also known as Aethelred the Unready, was the King of England during the late 10th and early 11th century. Here are some of the important issues and events of his reign:

Viking invasions: Aethelred's reign was marked by a series of Viking invasions. Despite paying large sums of money, known as Danegeld, to the invaders in an attempt to buy peace, the Vikings continued to ravage England. Aethelred was unable to effectively deal with these invasions and this led to his nickname "the Unready."

St. Brice's Day massacre: In 991, Aethelred ordered the killing of Danish settlers in England in an attempt to stem the tide of Viking invasions. This event, known as the St. Brice's Day massacre, led to increased hostilities between England and Denmark.

Political instability: Aethelred's weak leadership led to political instability within England. He was forced to flee to Normandy in 1013 and was replaced by Sweyn Forkbeard, a Danish king. Aethelred returned to England in 1014 and regained the throne, but he died the following year.

The rise of the Danelaw: During his reign, the Vikings established a large and powerful presence in England, known as the Danelaw. This area, which covered much of northern and eastern England, was ruled by Danish law and had its own system of government.

Church and Monastery: Aethelred was involved in several conflicts with the Church, including the murder of Saint Alphege, the Archbishop of Canterbury in 1012, which led to a temporary exile for Aethelred in Normandy. He also was known for his support of monastic communities and the building of monasteries.

Overall, Aethelred's reign was marked by a lack of success in dealing with the Viking invasions, political instability, and conflicts with the Church, which led to a decline in the power and prestige of the English monarchy during this period.