[From Wikipedia] Ari Gold is Vince's agent. Born in Chicago, he is a product of the public school system, and a self-described "lowly Harvard grad with a J.D./M.B.A. from the University of Michigan." Ari is Jewish and has one brother, Howard, and despite making multiple exaggerations of "a sister" of his that he has referred to as both crazy and a whore, Ari has stated that he has no sister.
Despite his position as one of the most powerful agents in Hollywood, Ari acquiesces to his wife at home (who we are led to believe has a large inheritance from her father), who is able to keep him in check. Despite frequent sexual innuendos, Ari says he has never cheated on his wife and "loves liars, but hates cheaters."
Towards the end of Season 2, Ari gets into a rivalry with Terrance McQuewick, his boss and the majority owner of the agency. Ari had been running the agency in Terrance's absence and had been confrontational with him over his desire to replace Ari as Vince's agent. When Ari attempted to break away from the agency along with eight other agents, he was ratted out by Adam Davies and was then terminated from the company. Later in the episode, he appears to have a brief mental breakdown but recovers after Lloyd lectures him and encourages Ari to continue his attempt to open his own agency. In Season 3 Part 1, Ari sets up a small boutique with five other agents working for him, until Terrance and Ari settle on $11 million dollars in return for Ari not suing Terrance for wrongful termination. Later on, Ari intends to use the money to start up a much larger agency, but he is found out. Terrance makes it clear he will spend all of his money to ensure Ari never sees a dime of their agreed settlement. In the end Ari's former mentor and former boss before Terrance, Barbara "Babs" Miller makes a deal to partner with him to start a new agency. It ends up being called Miller Gold Talent Agency. Ari comments that it sounds like the name of a beer company.
Ari and Eric Murphy are the primary influences in Vincent's life. But it is clear that Vincent trusts and follows Eric's advice much more than he does Ari's. This makes for a tense relationship between Eric and Ari. While neither one particularly likes the other, they realize that they are in a marriage of necessity and grow to become close comrades. Their personal and professional relationship shatters at the end of the Season 3 Part 1 finale when Eric and Vince fire Ari due to his risky business move that ends up costing Vince the role of Joey Ramone in a biographical film documenting the story of legendary punk rock group The Ramones'.
In the following episode, Ari had a friendly lunch with Vince and Eric, informing them that his dream project, Medellin (the story of Colombian drug kingpin Pablo Escobar), is now available, but Vince's new agent Amanda informs him that this is not the case. Later that night at Vince's birthday party, Ari and Amanda square off, but Ari backs off, knowing that he planted the seed of doubt in Vince's mind. Vince decides not to accept any new projects until he is certain that Medellin is off the table.
During the 17th episode of Season 3, "Return of the King," Ari informs Vince that Medellin has officially become available, and Ari tries his best to get the lead role for Vince, but because it is Yom Kippur, Ari has difficulty in doing so and the project is shut down. Vince, believing that Ari would've never let it happen, feels that Amanda let the deal fall through because of their relationship and that filming Medellin would keep him busy for six months. Either way, Amanda dropped Vince in every sense of the word. In the next episode The Resurrection, Vincent and Eric rehire Ari as their agent, since Ari got them the full rights to Medellin as they will be producing the project thus reviving the film.
During Season 4, Ari tries hard to get Vincent a job, but struggles to do so as everyone won't give him a job without validating Medellin first. Eventually, the trailer for Medellin is leaked, inducing a flood of offers. The film they decide upon comes from an adaptation of a book Eric gave to Ari some time ago. It is seen as a potential blockbuster for Vincent; Ari goes to Dana Gordon to acquire the role. However, the role is already filled, so Ari and Lloyd begin a game of sabotage to get Vincent the role, successfully after getting Heath Ledger to drop out. However, the intended director drops out as well. Ari, in a last-minute desperation, sells Dana Gordon the Dream Team: actor Vincent Chase, producer Eric Murphy, and director Billy Walsh. Billy gets commissioned to write the script, but deviates from the source material entirely. Ari then struggles to get the studio interested in the new Project "SILO" which, according to Vince, is a gold mine.
In the Season 4 season finale, Ari tries to sell Medellin before the screening, getting large offers, eventually the decision is made by the financier Nick Rubenstein, who has accepted an offer from Yair Marx (2nd of 3 people who wanted to finance the film - he did not finance it of course) to buy the film for $75 Million. After the screening the crowd at Cannes boos it, Marx drops his offer right then and there. Eventually Harvey Weingard, comes and buys the film for $1. Ari is confident that Harvey can fix the film.
In Season 5, after Alan Gray - the studio head of Warner Bros. - suffers a fatal heart attack, Ari is offered the chance to succeed him by the studio's chairman John Ellis for $10 million. Ari is not sure what to do: if he takes the job, he could give Vince any role he wanted with the studio but it would also mean that he couldn't be Vince's agent, which could also end their friendship. He decides to turn the job down, but then he learns that Amanda Daniels - who still holds a grudge against Vince and Ari - is next in line. Ari attempts to make peace with her, offering to put his full support behind her for the job as long as she agrees to add Vince as the second lead in Smoke Jumpers. Saying that Vince isn't good enough, she refuses the deal, adding that "[Ari] can kiss [his] relationship with the studio goodbye." Wanting to save his friend's career, Ari declares that he's taking the job to spite her, but instead convinces John Ellis to give the position to Dana Gordon. Not only does this guarantee Vince in Smoke Jumpers, but it also repairs his relationship with Dana.
After that was resolved, Ari meets with Andrew Klein, an old mentor and friend during Ari's day as an assistant to agents at Terrance and Jim Oliver's agency. Ari was ready to give up being an agent and go back to Chicago to become a lawyer, but it was his friend Andrew who convinced Ari to stay in Hollywood. When the partnership at the agency between Terrance and Oliver broke up, Ari went with Terrance but Andrew went with Oliver, who wound up ripping off his clients and employees. As a result Klein's status as a rising star was halted. Eventually, Ari convinces Klein to sell his profitable literary agency to Ari in return for Klein getting more responsibilities, more money, and a second chance at life as a big time agent like Ari. Unfortunately, Ari's partner, "Babs," disagrees with Ari's buyout plan, so Ari embarrasses Babs at a luncheon honoring her and powerful female agents. Ari proposes that the agency be split down the middle. Babs finally agrees to the purchase of Andrew Klein's agency, but tells Ari that any losses from the purchase will go on Ari's end of the books.
In Season 2 we found out that Ari was involved with Dana Gordon at some point before his marriage. In Season 5 Dana and Ari's relationship is confirmed to have occurred before he was dating his wife in the year 1990.