As mentioned before, Kenneth's first fell in love with Acting at age 15 where he saw the great actor Sir Derek Jacobi performing on stage the leading role of Hamlet. From there after he himself became obsessed with the theater, especially Shakespeare.
When he turned 18, he was offered places in the top drama schools of the UK. Places such as: the Central School of Speech and Drama, and the Royal Academy of Dramatic Arts. The second he did attend and was soon to become successful. Directly out of 'acting school' Ken got himself a part in the West End production of "Another Country". This performance won him plenty of awards at his young age.
Only a couple years later, he played Henry the 5th at age 23 for the Royal Shakespeare Company (RSC). Just at it did with his movie career, Henry V boosted his stage credits, making him recognized as an incredible young talent of the British stage. But he quite the company in the prime of his stage career, refusing another contract with them. I don't know all the reasons but I do know it had something to do with their bureaucratic aspects.
Finally he got together with David Parfitt, a friend he's made during his role in "Another Country". They formed a new company called "Renaissance" (Renaissance Theatre Company) in 1987, about the same time his movie career really kicked off. Only... it didn't start out so well... Ken made a huge mistake with the British press with his play that starred, was written and directed by Ken himself. It was called "Public Enemy" and had some of the worst reviews in his career. Most of them were slanderous of his overwhelming Ego and his 'over qualified' talents. Of course we all know that's not true.
However, the company's next few productions healed over most of the damage as he directed and starred in several Shakespearean greats, that included Twelfth Night, Much Ado About Nothing, and Hamlet. His stage Hamlet was never met as well as his movie Hamlet, which appeared a little later.
But although he was in the theater so much as it was, after all, his first love. He never stopped with the BBC's TV series and movies, and finally ended up on the silver screen, which is where he won most of his fame.