This topic (I'll just call it 'Plomb Empire and its long complex quagmire of subsidiaries and brands') is not one that can be waded into this lightly and without being explicit about dates. For beginners, "Challenger" was not acquired. The "Challenger" name is actually older than the "Proto" name (1948) and older than "PENENS"/"Fleet", too, which was established in 1942 as a contracting arm of the company that didn't start commercial sales until the late 1940's. "Challenger" dates to 1939, when the Plomb Tool Company used it for the first time to market a 3/8-inch drive socket set. For another example, there never was a Proto Tool Company. "Proto" was also a Plomb Tool Company brand. The Plomb Tool Company never changed its name to the Proto Tool Company. The Plomb Tool Company changed its name to Pendleton Tool Industries, Inc. in 1957. When Ingersoll-Rand bought the whole shebang in the 60's, they made it a division of IR called Proto Tools. That division was bought by Stanley. All of the various brands and subsidiaries (e.g., Proto, PENENS/Fleet, P&C, Challenger, etc.) belonged to Plomb, then PTII. Frankly, I don't know squat about the quality of any of them or how they were marketed after the mid 1950's.
EDIT: We had developed an excellent, detailed timeline on the old TA. If Todd was able to save it, I am sure he plans to re-post it on TA 2.0 at some point.