I walk by this plaque on my way home. It's on the north side of the building at Rainier & Edmunds, the Toby Building.
According to this National Park Service report, Simeon Toby spent time in Alaska during the Klondike gold rush. He built the building at 4850 Rainier Ave S in 1903, and added a third story about a decade later. In 1909 he opened a bank, and in 1922 he built the Rainier Valley State Bank building (today it's the Starbucks). He died in 1924.
Here's an excerpt from that report:
Simeon Toby, Columbia City banker, was active in the community and probably was remembered most for his efforts in convincing the city about the need for a road over Beacon Hill. In order to get to Georgetown and West Seattle in the early 20th century, it was necessary to either attempt to navigate a steep and muddy wagon road over the hill, or go all the way north to Dearborn Street and then back along what became Airport Way, at the base of Beacon Hill’s west edge. Efforts to lobby the Seattle City Council were successful, and Columbian Way was constructed on an almost straight northwest to southeast route from Spokane Street to Rainier Avenue. For his efforts, Toby was memorialized as “The Father of Columbian Way” on a large bronze, embossed plaque that was installed for many years in a small park at the northwest corner of Rainier Avenue and Edmunds Street, and later was moved across the street and installed on the north wall of the Toby Building. Buzz Anderson, Rainier Valley Historical Society president, noted that more of the credit for the establishment of Columbian Way should probably have gone to Ralph Nichols Sr., who resided in Columbia City and served on the Seattle City Council.
In 1932, according to Don Sherwood, the local Lions Club put up that handsome plaque, mounted in a stone tablet. I imagine the northwest corner of Rainier & Edmunds felt like an extension of Columbia Park — Mikala says the Columbia Plaza site behind it used to be an undeveloped hill.
But in 1956 this little park-like island and the remnant of 37th Ave S became a building site, developed by the successor to Toby's bank — Seattle First National Bank (SeaFirst, now Bank of America).