The Seattle Rainiers, originally named the Seattle Indians, were a minor league baseball team which played in the Pacific Coast League from 1903 through 1906, and from 1919 though 1968. Along with the Los Angeles Angels, Portland Beavers, Oakland Oaks, Sacramento Solons, and San Francisco Seals the Rainiers were charter members of the Pacific Coast League which was founded in 1903. Though the team finished second in 1906, the PCL contracted from six teams to four after the season (mainly due to the failures of the Sacramento franchise). For the next eleven seasons, the Indians played in the Northwest League, at the time a Class B league.

The Indians re-entered the PCL in 1919 with Portland (which had dropped out of the league after 1917), bringing the number of teams in the league to eight. The Indians finished in last place that year, but jumped to second in 1920. In 1924, the Indians won their first PCL pennant, clinching the title on the last day of the 202-game season.

For more than a decade after their championship run, the Indians were mired in the second division year after year. In 1932, their home park, 15,000-seat Dugdale Field, burned to the ground. Located at Rainier and McClellan Streets, it had been built in 1913 when the Indians played in the Northwest League. For the next six years, the team played at Civic Stadium, featuring a playing field of hardpan dirt.

Events took a definite turn for the better in 1938 when Emil Sick, owner of Seattle's Rainier Brewing Company, bought the Indians and renamed them the Seattle Rainiers. He began construction of Sick's Stadium, a 15,000-seat facility on the site of old Dugdale Field. Sick invested in the team, and it bore results. The Rainiers finished first in 1939, 1940, and 1941. They lost the postseason series in 1939, but won pennants in 1940 and 1941. In 1942 and 1943, the Rainiers finished in third place, but won the PCL pennant in the postseason both years.

After a few lean years, the Rainiers won PCL flags in 1951 and 1955, the last pennants won under Sick's ownership. After the 1960 season, the team was sold to the Boston Red Sox. The Red Sox in turn sold the Rainiers to the Los Angeles Angels in 1965, who renamed the team the Seattle Angels, as they were known during their last four seasons.

The last hurrah for the Rainiers-turned-Angels came in 1966, when the Seattle Angels won the championship of the PCL's new Western Division (the PCL had absorbed former American Association teams in the midwestern and southwestern parts of the United States). In the playoffs, the Angels defeated the Eastern Division champion Tulsa Oilers, for Seattle's last PCL pennant.

The team's last year was 1968, in which they finished in eighth place overall. Seattle had been granted an expansion team in the American League, the ill-fated Seattle Pilots, which began play in 1969. The Pilots would last but one year in Seattle, before a bankruptcy court sold the team to a group headed by Bud Selig and were moved to Milwaukee in 1970. In 1977, another American League expansion team was awarded to Seattle, the Seattle Mariners.