I don't know where I found the following, but it might be helpful in this thread:
"Proto was founded in 1907 by Alphonso Plomb, Jacob Weninger, and Charles Williams as the Plomb Tool Company, a small blacksmith shop making chisels in Los Angeles. In the 1930s, Plomb released what is commonly credited as the first combination wrench.
"Plomb acquired a number of companies during the 1940s, including Cragin Tool of Chicago, IL, in 1940, P&C Tool of Oregon in 1941, Penens Tool of Cleveland, OH, in 1942, and J.P. Danielson of Jamestown, NY, in 1947. Penens Tool would produce tools under the Fleet and Challenger brand names after its acquisition.
"In 1946, Plomb was sued by another tool manufacturer—Fayette R. Plumb, Inc., now a brand of Cooper Hand Tools — for trademark infringement. The company began manufacturing its tools with the Proto name, a portmanteau of "professional" and "tools," in 1948. In 1957, the company began operating as Pendleton Tool Industries.
"In 1964, Proto was acquired by Ingersoll Rand, and in 1984, it was acquired by Stanley and became Stanley Proto Industrial Tools."