This term came from a 1937 brand name of parts that were manufactured for Chrysler Corporation cars and is now considered a synonym for any Dodge, Chrysler, Plymouth, Imperial, DeSoto, Dodge Truck or Ram. What was the now-famous brand name?

Okay!

Mopar was an original equipment and replacement parts manufactured for Chrysler, Plymouth and Dodge automobiles. The name comes from the 1937 packaging of "Chrysler Motor Parts" antifreeze. The term MOPAR has become synonymous with any Chrysler-built vehicle: Dodge, Chrysler, Plymouth, Imperial, DeSoto, Dodge Trucks or Ram.

https://en.wikipedia.org/wiki/Mopar

Sorry, that is wrong.

Mopar was an original equipment and replacement parts manufactured red for Chrysler, Plymouth and Dodge automobiles. The name comes from the 1937 packaging of "Chrysler Motor Parts" antifreeze. The term MOPAR has become synonymous with any Chrysler-built vehicle: Dodge, Chrysler, Plymouth, Imperial, DeSoto, Dodge Trucks or Ram.

https://en.wikipedia.org/wiki/Mopar