While Mark only appeared in season 3, his reappearance in season 10 had a major impact after he catches Rachel and Ross carrying Rachel's possessions out from Ralph Lauren (she was fired for going on an interview with Gucci).Ross doesn't remember him at first, until Rachel reminds him, in which he declares, "I hate that guy! It was then revealed that Mark is married with twins, calming Ross all of a sudden.Mark did however find Rachel a job with Louis Vuitton leading to almost moving to Paris, Ross tries to bribe Mr.Zelner into re-employing her, finally allowing her to go after realizing how nervous and scared, yet incredibly excited she was.Mark was delighted when he found out and asked Rachel out on a date, making both Gunther and Ross angry in "The One With The Tiny T-Shirt", and Ross has to be talked out of attempting to intervene by Chandler, and is delighted when he later learns Rachel broke up with Mark after realizing she really only agreed to date him to get back at Ross for what he did (and Mark's attitude towards Ross throughout this discussion with Rachel shows that the dislike is mutual.) In "The One With Princess Consuela", Mark returned for the last time in the show where he found Ross and Rachel moving stuff out of her office.After he leaves, Ross seems to consider him a nice guy and asks Rachel if they had met.We are engaged on the issue and committed to looking at options that support our full range of digital offerings to the EU market.
Overhearing a whining conversation between Rachel and Monica he offers to help Rachel get a job alongside him at Bloomingdale's (Rachel was employed at Fortunata Fashions after quitting her job at Central Perk to pursue her fashion career).
Ross was jealous of Mark's relationship with Rachel and resentful of him.
Mark was always considered as an obstacle to Ross and Rachel's relationship and was happy when they broke up.
This results in Ross and Rachel having a fight at her apartment and then breaking up in tears.
The breakup obviously increased Ross's hatred of Mark.