A member of the Enterprise landing party on Gamma Trianguli VI in 2267, who is vaporised by a bolt of lightning directed by the machine intelligence Vaal.
Kaplan appears in the second-season episode The Apple, as one of the security detail accompanying Kirk, Spock, McCoy, Chekov and Yeoman Martha Landon to Gamma Trianguli VI.
Hendorff has already been killed by the darts of a pod plant when the sky darkens without warning. A storm gathers over the party, and a bolt of lightning strikes Kaplan where he stands, leaving nothing but a scorch on the ground. Spock is later hit by a second bolt and survives.
Kaplan is the second of four security men lost on the mission, the others being Hendorff, Mallory and Marple. The deaths lead Kirk to question his own judgement in staying on the planet. Kaplan was played by the stuntman Dick Dial.