Gregory B. Jaczko (/ˈjɑːskoʊ/;[citation needed] born October 29, 1970, Norristown, Pennsylvania) is a physicist who is the 13th and former chairman of the U.S. Nuclear Regulatory Commission (NRC) from 2009 to 2012.

[10] Jaczko has asserted that the greatest possible openness furthers the Nuclear Regulatory Commission's work on the protection of the environment and of public health and safety.

[10] He encourages “licensees, vendors, state and local governments, interest groups, and the general public” to participate in the commission's policy-making efforts.

"[15] At a House Government Reform and Oversight Committee hearing on December 14, 2011, NRC Commissioner William Magwood, a fellow Democrat, testified about what he called Jaczko's abusive behavior towards employees, especially female subordinates.

She sat, talking with her supervisor until she could calm down sufficiently to drive home.”[16] A report by the Government Reform and Oversight Committee detailed incidents indicating what was cited as Jaczko's "propensity for angry outbursts and aggressive behavior."

[2] On July 9, 2012, Jaczko was replaced by Allison Macfarlane, a nuclear waste expert and associate professor at George Mason University.

[3] In 2013 he was appointed by Harry Reid to a post on a Congressional panel overseeing the National Nuclear Security Administration[22] Gregory Jaczko has an important cameo appearance in the 2023 Documentary Film SOS: The San Onofre Syndrome directed by James Heddle, Mary Beth Brangan and Morgan Peterson.

On a recent interview[23] producer Mary Beth Brangan stated that it was the Fukushima accident what set her and her life partner James Heddle into the making of that film.

On the film, which issues a critical warning that America's 55 nuclear power plants, each with their own tons of intensely radioactive waste lasting millennia—in inadequate temporary containers with no plans to repair them—are putting their local communities and national security at grave risk, archival footage from a KPBS news show, Jaczko stated: "But frankly once they get loaded, I don't see them ever taking those canisters out of there.