Pioneers in Database Research
This could be viewed as a very speculative question. However, for the database community it should be a no brainer and a slam dunk.

Edgar Frank Codd : Inventor of the Relational Model we all model databases with.

Christopher J Date : Extensive writer of Database Theory. He keeps evolving database theory and expresses such in his current website.

Donald Chamberlin and Raymond Boyce : Authors of SQL

Some people say that Pioneers explore the land and take all the arrows, while settlers get to dwell in the land left by the trailblazing of Pioneers.

Other names can be added to this list, but database theory and research had its roots from the works of these Pioneers. All users of Databases after their inital works are like Settlers in the land.

Anyone can read books or Google names of such people, but nothing beats using the principles of relational theory to appreciate the depth of their research.