Yair Marx is an extremely wealthy man and international playboy from Israel. He is portrayed by Assaf Cohen.
Yair was described by Ari Gold as being a potentially "very dangerous man who might be a prince, an arms dealer, a coke dealer, who knows." Ari nervously says that Yair "could be Mossad or Hezbollah, neither would surprise him." After unsuccessfully pitching Sylvester Stallone as Pablo Escobar's father for Medellin, Yair offers to finance the film for 60 million dollars if Vince will sleep with Yair's wife, Nika Marx.
Yair was the second producer of three that wanted to finance Medellin for Billy, Eric and Vince. In the Season 4 season finale, Yair puts an offer to pay for their budget and then one for practically double the budget before the screening. After the screening he backs out saying he never signed any papers, telling Ari to sue his company but he won't get anything, since it's based out of Dubai.
- Despite the character being from Dubai, Yair uses Hebrew phrases such "Bo'na" (come here) an has a distinct Israeli accent.
- Yair's origins are never actually confirmed. While his company is based in Dubai, this does not necessitate his nationality. Many business people set up shop in countries other than their own.
- Yair Marx is referenced on the front page of The Hollywood Reporter (International Weekend edition, December 7–9, 2007). The cover story titled 'Reel Slick' discusses the rise of film financing via Mideast oil money.