Who is Colonel Robin Zacharias from Without Remorse and what is their importance?

Colonel Robin Zarcharias is a pilot. He served in Vietnam, where he was captured by the North Vietnamese, and later beaten, tortured, and questioned by a Russian officer. Robin is aware of other prisoners because he has seen some them. He has not, however, communicated with anyone. Due to the efforts of Kelly, Ritter, and others, Robin and the other prisoners are moved to a regular prison camp and later released.