I was torn between Boole and Godel.

It's obviously Frege in my opinion. Most logicians (so far as I can tell) agree that modern mathematical logic was a huge improvement on Aristotle's logic. Boole is clearly important too, but Frege's creation of Classical Logic is hard to top, and it was Frege's development of First-Order Predicate Logic that really got mathematical logic going (correct me if I'm wrong).

Although, I wish I could have voted for Priest as well, as he's a bit of a rock star of sorts lately, and wrote perhaps the standard intro text to Non-Classical Logics. I've found him to be quite insightful on logic generally, especially on questions such as how we decide what logics to work with.

... Frege's creation of Classical Logic is hard to top, and it was Frege's development of First-Order Predicate Logic that really got mathematical logic going (correct me if I'm wrong). — MindForged

Peirce independently and contemporaneously achieved the same thing - the introduction of quantifiers and bound variables. He wrote voluminously about the logic of inquiry, including abduction/retroduction and induction as well as deduction. He also was a pioneer in three-valued logic and greatly advanced diagrammatic systems of logic, although these contributions are not as well-recognized.

Peirce independently and contemporaneously achieved the same thing - the introduction of quantifiers and bound variables.

Well, several years after Frege if you want to get technical (1879 or 80, IIRC).

But while Pierce had better contemporary acknowledgements and influence (poor Frege), I think in the long run it was Frege who had more influence on logic. Like, his (and to a lesser extent, Dedekind's) Logicist program held a lot of sway in philosophy, maths & logic, at least until Gödel's work on incompleteness (although it still has some support, though perhaps no much). A lot of Russell's work was tailored in that direction, after all.

Imhotep

Peirce.

According to my own limited knowledge, I would say Kurt Gödel.