Who is Mac from Cities of the Plain and what is their importance?

Mac McGovern is the foreman on the ranch where John Grady and Billy work. The government is attempting a takeover of his land, but he is determined to keep working it until he is forced off.
Mac has a great appreciation for John Grady's ability to work horses and depends on Grady to make decisions when purchasing horses at auction. When Grady tells him he's planning to get married, Mac provides the couple with a little house he owns out in the hills. He also gives the Grady his late wife's wedding ring because John can't afford one.