Where did Marlin get its name?
As far as I know Erik van der Zalm started Marlin. He is from the Netherlands and Zalm translates to "salmon". One of the design goals of Marlin was to make it faster than the other firmware available at that time. And a marlin is a very fast swimming fish.

Some firmwares developed after Marlin also joined this fish theme: Sailfish, Minnow, ...