Terence Tao is a gift to the mathematical community. He is an excellent collaborator, a talented communicator, and one of the broadest and sharpest minds working today. Eighteen years ago, when he was just past thirty years old, he wrote the essay What is Good Mathematics?. I discovered this when Steven Strogatz invited Tao onto his podcast The Joy of Why to discuss how well this essay holds up.
Both of these are great, but start with the opening section of Tao’s essay, where he lists twenty-one ways to measure mathematics as being “good.” It displays his impressive clarity of thought and writing ability and evinces how the professional mathematics scene isn’t what one may have expected.