According to the Minnesota Historical Society, the first governor's fishing opener was likely held in 1948 at Mille Lacs, with Gov. Luther Youngdahl in charge. We say "likely" because, according to the MNHS, there's no evidence Youngdahl was actually there.
For the first 10 years, Mille Lacs hosted the event before it moved to Upper Red Lake in 1958. In 1961, Walker's Leech Lake was the host, and since then the opener has rotated around the state every May.
In 1963, the Minnesota media dubbed the event the "Governor's Fishing Party." That name stuck until Gov. Al Quie gave it the more formal name, the "Governor's Fishing Opener." "Party" apparently sounded too festive.
For a who's who list (governors/lakes/cities) of every opener since 1948, here's a link from the Historical Society.
And here's just a few photos, courtesy of the Historical Society, of ex-governors angling ... for fish:
1961: Ex-Gov. C. Elmer Anderson and Gov. Elmer L. Anderson --
1965: Gov. Karl Rolvaag with Iowa Gov. Harold Hughes --
1977: Gov. Rudy Perpich --
Finally, here's what the Fishing Opener looked like in the early 1960s, courtesy Alexandria's KCMT-TV. Some of the video is silent, with a few interviews later in the clip. But it's pure gold: