Lieutenant Ching, known on Earth as Dave Miller, is a Kryptonian man, a member of the Military Guild on New Krypton. He's assigned to be the bodyguard for Zara.
The two were sent to test Superman, to see if he was worthy of being married to Zara. (Lois and Clark: The New Adventures of Superman - "Through a Glass, Darkly") Among his tests are a bomb that could have killed hundreds of people and another which he said would destroy all of Metropolis. His ruthlessness is explained in "Big Girls Don't Fly": in addition to being faced with a potential civil war among the Kryptonians, for years he has had to help build a new settlement on an inhospitable planet. Moreover, the entire culture he was raised in is heavily utilitarian and places little value on love or kindness. The episode also explains his resentment towards Superman: Ching is deeply in love with Zara, who is betrothed to Superman through arranged marriage.