Oregon Gov. John Kitzhaber resigned Friday amid the growing influence-peddling scandal involving him and his fiancee, Cylvia Hayes, becoming the state's first governor to resign in disgrace.

In a letter to Secretary of State Kate Brown, Kitzhaber wrote that his resignation will take effect at 10 a.m. on Wednesday, Feb. 18.

Kitzhaber, a Democrat and Oregon's 36th governor, made his decision facing a state criminal investigation and a string of demands from top state officials to step down.

Kitzhaber's historic fourth term lasted just one month and one day, starting under a cloud of allegations that he and Hayes had abused his office, possibly committing crimes and ethics violations. The scandal only grew with revelations that Hayes was taking money as a private consultant and pushing the same policies in her public role as first lady.

Secretary of State Kate Brown, a fellow Democrat, will succeed Kitzhaber.

Kitzhaber's decision capped a bizarre and tumultuous week filled with speculation about his future. He had almost resigned Wednesday, summoning Brown back to Oregon from a national conference in Washington, D.C. But before their private meeting, the governor pulled back after discussing his decision with Hayes and his attorney, Portland lawyer Jim McDermott.

The turn of events was so unusual for Oregon that state officials initially didn't know how the chain of succession would work.

By Thursday, the former emergency room physician had lost support among even his allies. Senate President Peter Courtney and House Speaker Tina Kotek, both Democrats, met Kitzhaber for breakfast Thursday morning and told him it was time to go. State Treasurer Ted Wheeler labeled the situation "untenable" and also called for the governor's resignation.

"Clearly, Wednesday unnerved people and they looked around at what that unnerving had done and decided Kitzhaber had no political capital left," said Jim Moore, a Pacific University political science professor. "At best, he was holding on to the office as a political bargaining chip with a prosecutor."

Kitzhaber's decision cast a pall over his allies, who lamented the tarnished end to his long public service career and worried about the impact on his legacy.

"He is a friend. He is a son. He is a brother. He is a father. He is a human being," Courtney said. "It is all of these things for which I hope he is remembered. I hope all of these things are his legacy. He deserves that. Governor John Albert Kitzhaber, MD, I am sorry."

First elected to the Oregon House in 1978, Kitzhaber moved to the Oregon Senate two years later and served as its president through 1993. He was elected governor in 1994, 1998, 2010 and again in 2014.

His final term was plagued from the start with questions about Hayes' consulting contracts and Kitzhaber's handling of them, an issue that first came to light in an October investigation by Willamette Week.

As the controversy escalated, the governor was slow to release government records and reluctant to answer questions about Hayes' role in his office.

Late last week, Oregon Attorney General Ellen Rosenblum opened a criminal investigation into Kitzhaber, 67, and Hayes, 47, who were also named in three ethics complaints filed last year with the Oregon Government Ethics Commission.

At a Jan. 30 press conference, Kitzhaber assured constituents that he and Hayes planned to cooperate with the Ethics Commission, adding that it was the appropriate body to answer all of the outstanding questions. Yet behind the scenes, the governor's attorneys were arguing that the case should be dismissed because Hayes was not a public official.

Kitzhaber's grip on his office began to dissolve after he stumbled through the press conference, looking visibly nervous and cracking jokes that landed flat.

"This may begin to sound like an interview with Marshawn Lynch," he said at one point, referring to the Seattle Seahawks running back famous for refusing to answer reporters' questions.

-- Rob Davis

rdavis@oregonian.com

503.294.7657

@robwdavis