Who is Dan Cody? Dan Cody was Gatsby’s best friend. Gatsby also has a picture of him hanging in his wall. Gatsby’s new life began on the lake when he met Dan Cody. Dan Cody was a wealthy copper minor from Montana. Cody and Gatsby sailed around the world three times over the next five years. During this time, Gatsby served as steward, mate, skipper, and secretary for Dan. Gatsby chose then to abstain from alcohol forever after witnessing the destructive behaviors of Cody during his periods of drunkenness. Gatsby even had to jail Cody on occasion to prevent him from committing dangerous acts.
Dan is a somewhat coarse man who became immensely wealthy during the Gold Rush. He mentored Gatsby when he was a young man and gave him a taste of elite society. He taught him how to do business and he taught him all he new. Dan Cody also left Gatsby a large amount of money before he died because Gatsby had helped him and had taken care of him. Gatsby used this money to start the business that he is in now. And he uses what Dan Cody taught him to run his business. (http://www.novelguide.com/thegreatgatsby/characterprofiles.html)