Captain Walter Granger was a male Human in the 22nd century from Earth.

In 2123, Granger commanded the Earth ship SS Mariposa on a colonization mission to the Ficus sector, with a mixed group of colonists ranging from Irish Neo-Transcendentalists to technology-savvy scientists.

Following the departure of the Neo-Transcendentalists on Bringloid V, the Mariposa crash-landed on a class M planet in a neighboring system, one-half light year from the Bringloid system. Only five individuals survived the crash, including Granger. After founding the Mariposa colony, he and his fellow survivors resorted to cloning to survive. In 2365, one of his clones, Wilson Granger, was the colony's Prime Minister while another, Victor Granger, was the Minister of Health. (TNG: "Up The Long Ladder")

This character was only mentioned in dialogue.
The clones of Granger were played by Jon De Vries, so we can assume that Captain Granger also looked like him.