Christian Johann Doppler (1803-1853) was a Austrian physicist. He became professor of experimental physics at Vienna.
He described the Doppler effect, the change in frequency (and thus also wavelength) of a wave due to relative motion of its source and observer, as for example in the change in pitch of an ambulance's siren as it approaches and then recedes.
Why is Christian Doppler famous?
Christian Doppler was an Austrian mathematician and physicist who discovered the Doppler Effect.