Given the task definition and input, reply with output. In this task, you are given a question. You have to answer the question based on your information.

The first Battle of Reading took place following an invasion of Wessex by the Danes, led by which Viking leader?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Bagsecg