Who was responsible for the initial heavy lifting in measuring the recessional velocities of spiral nebulae decades before Hubble related velocity to distance?

Answer

Vesto Slipher

While Edwin Hubble is famous for establishing the proportionality between velocity and distance, the crucial preliminary work of determining these velocities was largely completed by astronomer Vesto Slipher much earlier. Slipher painstakingly observed dozens of the enigmatic 'nebulae,' measured their redshifts, and established the critical finding that nearly all of these objects were moving away from the Earth, providing the necessary velocity catalog ($v$) for Hubble's subsequent distance correlation.

Who was responsible for the initial heavy lifting in measuring the recessional velocities of spiral nebulae decades before Hubble related velocity to distance?
Hubblegalaxiesastronomyredshiftdistance measurement