Short answers, pulled from the story.
Tom Ridge became the first Secretary of Homeland Security on the 24th of January 2003. He previously served as Governor of Pennsylvania before President George W. Bush appointed him to lead the Office of Homeland Security.
Congress passed the Homeland Security Act in November 2002 to merge twenty-two federal organizations into a single Cabinet-level department. The new entity officially opened its doors on the 6th of January 2003 following the terrorist attacks of the 11th of September 2001.
Alejandro Mayorkas assumed office on the 2nd of February 2025 after receiving a Senate vote of 56, 43. He left office on the 25th of January 2025 following this confirmation process.
As of the 8th of November 2019, the official order placed the Deputy Secretary first followed by the Under Secretary for Management and then the Commissioner of U.S. Customs and Border Protection. This statutory framework allows the secretary to directly establish an alternate order of succession outside normal provisions.
President George W. Bush nominated Bernard Kerik for the position in 2004 but withdrew his nomination just one week later because he had employed an illegal immigrant as a nanny. This employment disqualified him from holding federal office under existing laws.