Who is Tex Travis from The Log from the Sea of Cortez and what is their importance?

Tex Travis is the engineer on the three-person crew of the Western Flyer. He was hired in Monterey to join the expedition to the Sea of Cortez. Steinbeck describes him as thoroughly identified with the engine when aboard ship. He sleeps peacefully when it is running well, and he is physically pained when it is broken or in disrepair.