Former Oregon Secretary of State Bill Bradbury, who established the state's first-in-the-nation system of voting by mail, died Friday. He was 73.

Bradbury also advocated for environmental issues and ran for governor, all while battling multiple sclerosis for more than 40 years.

He died after unexpected medical complications during a six-month, around-the-world cruise with his wife of 36 years, Katy Eymann.

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"Bill Bradbury may be gone, but he leaves behind a legacy in Oregon that will endure for generations to come," U.S. Sen. Jeff Merkley said in a statement.

Bradbury served 15 years in the Oregon Legislature, retiring from the statehouse in 1995 to fight the shrinking of salmon populations. Known as "Mr. Fish," he served as director of For the Sake of Salmon until 1999, The Oregonian reported.

Bill Bradbury in OR

Bill Bradbury, center, holds hands with his wife Katy Eymann as he gets sworn in as Oregon's secretary of state by Supreme Court Justice Ted Kulongoski in Salem on Nov. 8, 1999.  (AP Photo/Don Ryan, File)

Gov. John Kitzhaber appointed Bradbury that year to be Oregon’s 23rd secretary of state. Bradbury served for a decade, focusing on improving Oregon’s voting system and establishing more transparent campaign practices.

Bradbury established Oregon’s vote-by-mail system, which has significantly increased voter participation since 2000. He also helped establish Oregon’s online political campaign contributions system, ORESTAR, which gives the public access to campaign finance information.

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He ran for governor in 2010, losing to Kitzhaber in the Democratic primary.

Those who knew Bradbury said he was always optimistic despite his condition, which can cause extreme bouts of fatigue.

"In battling MS with his trademark relentless optimism, Bill showed all of us how to bring good cheer and inner toughness to life’s many challenges," U.S. Sen. Ron Wyden wrote on Twitter. "He will be hugely missed."