Lieutenant Carl Jaeger was a male Human Starfleet officer who lived during the mid-23rd century. He served in the sciences division aboard the USS Enterprise under Captain James T. Kirk, during a historic five-year mission that starship undertook. He was one of the ship's meteorologists, and was fluent in the German language.
In 2267, Jaeger was among a landing party that beamed to the surface of Gothos to search for the missing Captain Kirk and Helmsman Sulu. At the time the landing party was assembled, climactic conditions were thought to be extremely inhospitable, and his expertise in geophysics served the landing party well.
Trelane recognized Jaeger's German heritage, gave a smart salute, and spoke to him in German, saying "Ein Deutsch Soldat, nein? Ein, zwei, drei, vier, gehen wir mit dem Schießgewehr!", while miming a military march. In response to Trelane's question ("A German soldier, no?"), Jaeger replied that his specialty was as a scientist, not as a military man.