I am very glad you liked The Lion etc and it was nice of you to write and tell me. The idea in my mind was, "supposing there were other worlds, and if one of them was like Narnia - and if it needed saving - and if Christ went to save it as He came to save us - let’s imagine what shape and name He might have taken there". And the answer was Aslan.
C. S. Lewis
--from his book Letters to Children, but a transcript
can be found on the blog Letters of Note.