Soviet mathematician and outstanding mathematical educator. He is the founder of Leningrad school of real variable function theory, and a series of work in function measure theory makes him a first-class mathematician in this field. Fitzgerald devoted his life to mathematics teaching. Love teaching and attach importance to teaching. He worked in Leningrad University (now St. Petersburg University) for more than 40 years, and until he retired in 1953, he was the head of the teaching and research section of mathematical analysis. He has taught mathematical analysis in universities for more than 30 years and trained many world-famous Soviet mathematicians. He is also enthusiastic about middle school mathematics teaching in the Soviet Union, giving lectures to middle school students and middle school teachers. He was the maker of the syllabus of Soviet middle schools in the 1930s. The founder of the first Soviet Mathematical Olympiad (1934) was also one of the organizers of the Soviet Teachers College. The three volumes of calculus courses are the crystallization of his teaching experience and teaching art. People praise "every class of his is a masterpiece of teaching, even his blackboard writing is like a work of art" and evaluate him as "a sincere, kind, highly responsible genius".