Sam Katz lost three times as a Republican candidate for mayor of Philadelphia but then found success producing documentary films about the history of his hometown.

That history now has Katz talking up Rudolph Blankenburg as one of the city's best mayors in the 20th century.

Rudolph who?

Blankenburg, a Keystone-Democrat, stunned the Philadelphia political machine in 1911 by defeating Republican George H. Earle Jr. by just 4,495 votes.

Blankenburg pushed for reforms in his single term that Katz calls "hugely impactful."

Katz on Thursday said he recently mailed in the paperwork to change his voter registration from Republican to independent.

Katz has roamed across the political spectrum in recent years, switching from Republican to independent in 2006 and later to Democrat before returning to the Republicans.

Katz tweeted this about his evolving political affiliation Thursday: "Changed my party registration to 'Independent,' a change that better fits my independent thinking and who I am. More to follow."

Does he plan to follow in Blankenburg's footsteps and challenge the city's political machinery with a third-party run for mayor in the general election?

"I don't know the answer to that question," responded Katz, adding that he would spend the next weeks and months releasing ideas "that run against the grain" of current thinking about how to improve Philadelphia.

"I feel like this is the right place for me politically," he said. "I intend to make some ideas public and to do so as a person of independent thinking."

Democratic candidates for mayor include State Sen. Anthony H. Williams, former District Attorney Lynne Abraham, former Councilman Jim Kenney, former Common Pleas Court Judge Nelson Diaz, and former PGW spokesman Doug Oliver.

Former State Sen. T. Milton Street Sr. has said he will formally declare his candidacy next week.

The Republican City Committee is still in discussions with potential candidates for mayor.

brennac@phillynews.com

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@byChrisBrennan