Commander Donald Kaplan was the chief engineer of the USS Intrepid in 2370.
Kaplan attended Starfleet Academy with Geordi La Forge; since that time, the two engineers had a friendly rivalry, regularly engaging in contests to see whose vessel had more efficient power conversion systems. When the Intrepid achieved a power conversion level of 97.1%, higher than was achieved on the USS Enterprise-D, he sent a message to La Forge that, in part, read "Maybe you should try cleaning your plasma grid once in a while." (TNG: "Force of Nature")
This character was only mentioned in dialogue.