Logan Sanders is a businessman and heir to his father's group of companies and was a client of Pearson Specter, particularly Harvey Specter's. He was the married man that Rachel Zane once had an affair with.
Logan took over the family business when his father decided to retire. Not wanting to "remain a dinosaur" and decided to start with a hostile takeover of Gillis Industries. Because of this move, Harvey had to let go of Sidwell Investment Group because of a conflict, after Mike Ross, also interested in buying Gillis Industries, put them in review.
After Harvey found out that Logan made a move on and kissed Rachel, who he knew was with Mike, Harvey let go of Logan Sanders & his company as a client.