Who is Mr. Jackson in Of Mice and Men?

I had to read Of Mice and Men, during the summer and then complete a packet. In the packet, it had a section where I had to characterize all of the characters, and one of them being Mr. Jackson, and I have no clue who he is. I read the entire book cover to cover, and there is no mention. I even sought out Wikipedia, but still I have no clue who he is! Please help me!