When we say that someone is “the father of _______”, we mean that they helped to found that subject.
One of the classic examples is the father of computer science, which is widely accepted to be Alan Turing. Turing created the first computer and helped the Allies understand the power of computing during World War II.
When it comes to the father of English, it is difficult to say. There is not a single person that helped found the English language. However, William Shakespeare is sometimes called the father of the English language. While he seemed to use several new words that did not exist before he wrote his plays, it is difficult to know whether he was truly the first person to use those words in context.
Some other people say that Geoffrey Chaucer is the father of English literature, because he wrote so much poetry during the Late Middle Ages. Some of his most famous works are “The Canterbury Tales”, which I coincidentally studied when I was in high school in my English class.
Still some other people call Lindley Murray the father of English grammar, because he was the first person to write down English grammar rules in 1975.
That being said, there is no single person that is said to be the father of English, the way that Turing is the father of computer science, Daniel Kahneman is the father of behavioral economics, or John Watson is the father of behavioral psychology.
English is simply too large a field with a history that stretches too far back to know for sure.
Geoffrey Chaucer, known as the Father of English literature.