Gottlob Frege is, along with Bertrand Russel I suppose, considered to be the founder of analytic philosophy. Along with that is his development of symbolic logic, the first real alternative to Aristotle’s syllogistic logic and also an important step towards computer science as we know it. He also got the ball rolling on the attempt to prove that mathematics is reducible to the laws of logic – an attempt which proved disastrous. You can’t win them all.
Frege is, along with Aristotle and Aquinas, something of a philosophical hero for me. Essays like, “Sense and Reference” and “The Thought” are essential reads. I also think he is kind of wrong on one very big subject: his analysis of the concept of existence/being. Well, it’s not so much that it’s wrong per se, so much as it is a very narrow account, reducing the meaning of the concept to a purely quantitative use. That there are analogical uses of the concept of being, and that we can use the concept to refer to a certain primal reality of thatness and that from that we can develop a metaphysics of being, just gets swept under the rug. I would like to go into more detail about this, but I’ve got to keep on the ball with my exams.