Merck’s Ken Frazier, one of just four Black CEOs in the Fortune 500, will retire on June 30.

Why it matters: His departure leaves just three Black people atop America’s 500 largest companies (assuming no other Black chiefs are named by then).

Details: Robert Davis, the company’s CFO and a white man, will take over as head of the pharmaceutical company.

• Frazier has been at the helm of Merck since 2011 and with the company since 1992. He’ll stay on as executive chairman for an undetermined period of time.

Flashback: Frazier was the first to quit former President Trump’s CEO advisory councils, following Trump’s refusal to condemn white supremacists in Charlottesville in 2017.

• The move led a cascade of CEOs to do the same. The councils were eventually disbanded.

The bottom line: When Frazier departs, the number of Black Fortune 500 CEOs will shrink to Rosalind Brewer, who takes over as Walgreens' top executive next month, Marvin Ellison (Lowe’s) and René Jones (M&T Bank).

• TIAA’s Roger Ferguson will step down next month.