There were three Mid-Nite's.
Charles McNider
Elizabeth Chapel
Pieter Anton Cross
Pieter Cross is the current Dr. Mid-Nite and still serves with the JLU from the time he took the mantle from McNider. He has a methuman ability to perfectly see in the dark, and serves and a highly expert surgeon. And can only see in the dark, so he has special lences which inable him to see in the light. Mid-Nite also carries in his gaunlets ton of medical equipment and is one of the best fighters in the DCU.
Here's one of my favorite pictures of him.