I’ll go with James Clerk Maxwell .. He doesn’t get as much recognition as Einstein or Newton but I reckon his work has easily had as big an impact on the way we live now. He worked out that electricity and magnetism are part of one phenomenon which he called electromagnetism.
He then made the crazy leap to work out than light was actually a combination of electric and magnetic fields and he put the whole thing in 4 surprisingly simple equations. Even scientists think its better to have fewer equations!!
We use those equations all the time when we’re studying the plasma trapped in the magnetic field of a fusion reactor. Without his ideas we wouldn’t be have mobile phones or the internet.. we wouldn’t have ‘I’m a scientist…’! 🙂
David Attenborough is probably one of the most influencial – he brought nature, science, climate change, geography and wolrd phenomina into peoples’ livingrooms and made some very complax things easy to understand for everyday people – whether you like science or not he could bring it alive and make it real. Engaging people in your research is sometimes difficult, but he did it extremely well.
I would also go with Jack’s favourite scientist James Clerk Maxwell since if it was not for him we would not have related all energy changes and currents to time and hence we would not have such advances we have today … mobile phones, TV and video signals and everything to do with electricity and communication!!