Alexei Vladimir "Alex" Filippenko (/fɪlɪˈpɛnkoʊ/; born July 25, 1958) is an American astrophysicist and professor of astronomy at the University of California, Berkeley.

His research focuses on supernovae and active galaxies at optical, ultraviolet, and near-infrared wavelengths, as well as on black holes, gamma-ray bursts, and the expansion of the Universe.

Filippenko's early work showed that the nuclei of most bright, nearby galaxies exhibit activity physically similar to that of quasars, driven by gas accretion onto a supermassive black hole.

In 1997, the Canadian Astronomical Society invited him to give the Robert M. Petrie Prize Lecture for his significant contributions to astrophysical research.

He was recognized in the 2007 Gruber Cosmology Prize for his work with then Miller Postdoctoral Fellow Adam G. Riess and for his highly specialized contributions in measurement of the apparent brightness of distant supernovae, which accurately established the distances that support the conclusion of an increasingly rapid expansion of the universe.

In addition to recognition for his scholarship, he has received numerous honors for his undergraduate teaching and public outreach, including the 2007 Richtmyer Memorial Award given annually by the American Association of Physics Teachers and the Carl Sagan Prize for Science Popularization by Wonderfest in 2004.

[27] In April 2015, Filippenko forwarded an email message from UC Santa Cruz Professor Sandra Faber regarding the controversial construction of the Thirty-Meter Telescope on Mauna Kea.

In that message, Faber stated that "The Thirty-Meter Telescope is in trouble, attacked by a horde of native Hawaiians who are lying about the impact of the project on the mountain and who are threatening the safety of TMT personnel.

[28] Faber encouraged astronomers to read more about the TMT protests [29] and to sign a pro-TMT petition written by Mailani Neal, a native Hawaiian high-school student.

[32] The American Astronomical Society issued a statement reiterating its formal anti-racist stance and noted the disagreement over whether Filippenko's apology was indeed "sincere and unqualified.