As a child it was Hawking as his book was the first one that really influenced me.
Right now it’s Ben Goldacre as I think he is doing something for science that research can’t do alone: campaigning for ethical publication and making sure we can trust what we read. This is the thing I hold most dear in science. That is, never ever making anything up for any reason.
I didn’t have a favourite scientist as a child, but there was this journalist on the Italian tv called Piero Angela who presented a very cool show called Quark, it was all about science. I think that show was what really got me interested in science at the beginning. Now my favourite scientists are other chemists a couple of examples are J.J. Gooding and D. Leigh.