Explain the significance of Alfred the Great for the development of English identity.

Great question! Alfred the Great was really important to the development of English identity, and is often remembered as a great English king—even though he wasn't really a king of England, because England as a defined country didn't yet exist. Alfred started out as King of Wessex, a historic county-kingdom within what is now southern England, and subsequently became the king of all the Anglo-Saxons. Alfred's key contribution to English identity can be best understood in relation to his influence on language, given how language influences identity. What united the Anglo-Saxons was their common language; at the beginning of Alfred's reign, though, even this was very loose, with multiple dialects warring within the Anglo-Saxon region. Alfred was extremely committed to the development of a united Anglo-Saxon tongue, particularly a semi-uniform written version of the language, and what he achieved in this arena helped those who spoke Anglo-Saxon to see themselves as a single people. By calling himself King of the Anglo-Saxons and defining a language for those Anglo-Saxons, Alfred created an idea of nationhood where one had not previously existed.
Alfred's reign was a turbulent one. The island of Britain was still constantly beset by would-be invaders, and Alfred was able to see off Viking attacks and establish himself as a dominant ruler. This already meant he was viewed as a very strong king within the Anglo-Saxon culture in which he lived, but more important was what he then did with his power. Alfred reformed the legal system in his new lands so that it was uniform—and fair. He was also very concerned with the idea that everyone should understand the religion they professed to follow (a religion that, of course, was very new). He felt that it was impossible to expect people to follow a religion that was taught in Latin, a language outside the reach of normal people. As such, under Alfred's reign, literature in English began to be produced en masse. Over this period, people came to understand themselves as "English" because they shared several common factors, including:
Adherence to Alfredian legal codes;
Speaking Anglo-Saxon, now the language of primary education; and
Adherence to the Christian religion.
These unifying factors helped create a sense of a larger kingdom where several had previously existed. By the end of Alfred's reign, emphasis upon written English also meant that Anglo-Saxon, although it still had variant forms, had reached a sort of standard. The extent to which this was important for the idea of identity can be seen through the attempts made by the Norman invaders to suppress and dismantle English when they invaded in the eleventh century. They did not want to encounter a unified English people with a common language. As such, they removed the language from use in court or legal settings, replacing it with French. During this period, English went underground, and once again came to divide into multiple dialectal forms so that the English would see themselves as a defeated and subordinate class ruled by the French-speaking Normans. However, it did survive in parochial settings, and the English identity Alfred created was strong enough that, several centuries later, it would once again oust Anglo-Norman as the language of court and the English people.