The question is a bit vague. If you are making a subjective, aesthetic argument then each of these posts make a great case. As far as importance to the development of literature and the English language, Geoffery Chaucer has to top the list. Even though The Canterbury Tales is unifinished, there is not denying its importance to language, poetry, and even (it's a stretch) the detective novel. Chaucer's use of the common language at the time (Middle English rather than Latin), realistic characters that defined an era, and wickedly clever narration make this work a literary powerhouse. He opened the door for every writer after him and made great literature accessible to all.
This is like asking me which one of my boys is my favorite LOL...it cannot truly be done. If I absolutely HAD to choose, I would choose William Wordsworth (who was one of the first British poets that brought poetry to the common man) and Robert Frost.
I think that one of the most influential writers in the English language is Walt Whitman. Whitman took a stodgy form (metered poetry), and made it accessible to everyone. "Leaves of Grass" is a beautiful celebration of the connectivity of the universe. His impact on poets today is pervasive, and his ideas were courageous and revolutionary.
I have to add the translators of the King James Version of the Bible. No, they didn't write the Bible, but anyone who has read modern translations of the Hebrew and Greek would have to agree that the KJV cannot be matched for its style and the beauty of its language. Other than Shakespeare, who has been quoted more often?
I would go with Dickens (England) if we're talking about a larger output, or Dreiser (America) in the same category. Both of them present grand pictures of the society of their times --- and each of them has LOTS of critics :)
Of course, I hasten to add that answering this question is impossible :)
I agree with post #2, but I also have to vote for Mark Twain. I love his humor and sarcastic views, but also the delicate and honest way he dealt with racism in America when slavery was still so contemporary.
I also love Jonathan Swift and Samuel Johnson. Two more smart alecs who are near and dear to my heart.
I would have to go woth Edger Allen Poe because his poetry was very well written and he had elements in his stories that no one else had in theirs
I am not entirely clear on the term 'English' but I would have to say my favorite American author is Emerson. I enjoy teaching the Transcendentalist and what they stood for. My students enjoy the projects that come out of that unit. Another one of my favorites is Edgar Allan Poe. How could he not be included. His psychological fiction just makes my skin crawl.
My favorite British writer would have to be Mary Shelley. I know, I know... she only wrote one really great novel but that one novel was the beginning of an entire genre that is still so popular today. The back story on the novel is also a great story to tell my students and they enjoy writing their own 'ghost stories.' Another one is Jonathan Swift. His satire is some of the greatest.
I believe that John Milton is also a great writer in English Literature. No, his works do not have the number of readers that Shakespeare, Poe, Twain, or even Dickens have, but he did go blind and wrote his entire "Paradise Lost" blind. He dictated that to someone and was never redundant. Even we, as seeing beings, are likely to use redundancy in our writings.
Without a doubt it is the great literary giant author of Beowulf, Sir Gawain and the Green Knight, Get Up and Bar the Door: Anonymous. In seriousness, I would be torn between Geoffrey Chaucer and Jane Austen. Chaucer brought literature to the people for the first time. Not only was it not in Latin, but it was about topics they recognized, could relate to, and would have enjoyed. The satirical view of life in the Middle Ages from The Canterbury Tales alone is invaluable. For Jane Austen, her canon is simply incredible. Not counting how difficult it was for a female novelist to be successful, she really explodes this genre onto the scene.