My favorite first book was Black Beauty. It left me with a love of animals which will last for ever.

Other books which have influenced me as an adult are Herodotus,
The Moon is a Harsh Mistress by Heinlein,
Oedipus by Henry Treece;
anything be Lewis Carrol especially "The Hunting of the Snark"
Trapps War by Brian Callison.

I read a lot of Algernon Blackwood and Dennis Wheatley as a teenager but grew out of those.

I read just about every Zane Grey that I could find. Then there was Hammond Innes and Alistair Mclean and Desmond Bagley.

Then there are those books that were part of the family when we were kids. Dad bought a copy of "The King's English Dictionary" just before they got bombed out during the war and he never had to pay for it, we thumbed through it over and over again looking at the illustrations. The poor thing looked quite pathetic when we had done with it. He also had 1001 gems of English poetry which we must have read 1001 times.