Which famous physicist taught Gregor Mendel at the University of Vienna?

Christian Doppler taught Gregor Mendel physics at the University of Vienna. Mendel studied there from 1851 to 1853 after his abbot arranged advanced training that would prepare him for teaching and scientific work.

Doppler was an Austrian physicist and mathematician best known for the Doppler effect, the change in a wave's observed frequency caused by relative motion between the source and observer. He published his explanation of the phenomenon in 1842, several years before Mendel arrived in Vienna. Mendel encountered him as a professor of experimental physics.

Mendel's education in Vienna also exposed him to mathematics, botany, and methods of careful measurement. Although Mendel is remembered primarily for genetics, his later pea experiments depended heavily on the quantitative habits he developed through science and mathematics. He returned to Brno in 1853, and from 1856 onward conducted the breeding studies that eventually established the foundations of modern genetics.