Mathematical Logic is something that has a very long history behind it. It has been debated on for many centuries. If someone were to divide mathematical logic into groups they would get two major groups. Both groups are very long. One is called "The history of formal deduction" and it goes all the way back to Aristotle and Euclid and other people who lived at that time. The other is "the history of mathematical analysis" which goes back to the times of Archimedes, who was in the same era as Aristotle and Euclid. These to groups or streams were separate for a long time until Newton invented Calculus, which brought Math and logic together.
Somebody who studies mathematical logic and gives his or her own concepts about it is called a logician. Some well known logicians include Boole and Frege. They were trying to give a definite form to what formal deduction really was. Aristotle had already done such a thing but he had done it with language, Boole wanted to do it with only Symbols. Frege came up with "Predicate Calculus".
As time went on people did not make new theories as much as they used to in the time of Aristotle. They mostly concentrated on expanding on theories that have been said centuries ago, proving those theories or putting them into symbolic form.
Table of Logicians*