Richard Phillips Feynman 🙂 Not only he revolutionise quantum mechanics and our understanding of it but was a great communicator and scientist who knew how to deliver the message to large audiences without losing their attention and the time entertaining and benefiting them!
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…’!
Definately Alexander Flemming. He was a Scot who discovered penicillin in 1928. He is renowned as one of the top 100 scientists of the 20th Century. Before his discovery of antibiotics people died from infections caused from a mere scratch, or simple toothache which could develop into an abscess!!! 🙁