Oscar Martinez is an accountant at the fictitious paper distributor Dunder Mifflin. He is an American-born Latino of Mexican descent, whose parents emigrated from their home country. Oscar is also openly gay after being involuntarily outed by his boss, Michael Scott. Oscar is calm, intelligent, and hard-working, though occasionally weary of his boss.
Oscar has worked at Dunder Mifflin for over nine years. He is openly gay (after being publicly outed by Michael) and lives with his partner, Gil (Michael once said: "I wonder if he (Gil) knows (he's gay)". Originally, Oscar was in the closet, and Gil was believed to be his roommate. In earlier seasons, he is seen driving a Saturn Ion. However, he is seen in the third season driving a Lexus RX 400h, a company car he was lent as a result of his unwanted outing by Michael. Oscar is the winner of the "Show Me The Money" award at the 7th Annual Dundie Awards.
Though Oscar is openly gay in later episodes, in the episode "The Fire", when asked by Jim "Who would you do?", Oscar offers the answer, "Pam"; also, in "The Client", he makes a passing reference to a woman he previously dated. It is unclear whether these references were meant to fool his coworkers as to his true sexual orientation, as he was in the closet at the time, or if it had not been decided yet that his character was gay (it was not revealed to the audience until Dwight discovered Oscar and Gil returning from a shopping trip, though Dwight was oblivious).
In a deleted scene from "Gay Witch Hunt", Oscar explains that he in fact notified Michael of his homosexuality during his job interview. This caused Michael to laugh repeatedly, and he hired Oscar on the spot because he was "the funniest person that [Michael] had ever met". Oscar then hid his sexuality from his co-workers (until he was outed) for fear of losing his job.
One of his most notable quotes is "What are you implying?"
In the episode "Diversity Day", Michael makes an example of Oscar in a diversity training seminar for his being Mexican. Michael also believes that "Mexican" is offensive, and he asks Oscar if there is a "less offensive" term, which Oscar explains that the term is not offensive. In "The Alliance", Oscar goes around the office asking for donations for his nephew's walkathon for cerebral palsy. Michael, scoffing at the low amounts the other employees have given, donates $25, not realizing that the donation amount is supposed to be per mile. Once informed of this by Jim Halpert, Michael tries to get it back but Oscar is angry that he is un-donating to a charity. But once Michael has ruined the day (again) he decides to donate that money, to make himself look better. In "Basketball", Oscar asks to be on Michael's team; however, Michael assumes he is good at baseball and boxing, but not basketball.
One of Oscar's favorite pastimes at work is playing a paper football game dubbed "Hateball" (because Angela hates it) with Kevin Malone whenever Michael isn't around. He keeps a two-year running total of their scores. Oscar enjoys ice skating, likes the office thermostat to be set to a chilly 66 degrees, and dressed up as a woman on "Halloween". He has a conflict with Angela Martin over her poster of babies dressed as jazz musicians and claims it offends him more than "hardcore porno." In "The Secret," Oscar calls in sick, but Dwight discovers that Oscar spent the day shopping and ice skating with his "roommate" Gil. Though Oscar successfully keeps his homosexuality secret from his co-workers, one subtle indication of his sexuality can be observed in the episode "Valentine's Day" when Oscar receives a gift and unconvincingly tells Kevin it is from his mother.
In the first episode of the third season, "Gay Witch Hunt", Michael obliviously calls Oscar "faggy" for preferring the film Shakespeare in Love to Die Hard. Oscar takes it personally and reports it to corporate. When Michael realizes Oscar is actually homosexual, he tries his best to make it up to him and learn to embrace the gay culture. Michael calls a meeting and announces Oscar's homosexuality in front of the entire staff, much to Oscar's shock and dismay. In the conference room, to show no hard feelings, Michael hugs Oscar then proceeds to try to kiss him. Oscar is both disgusted and horrified by Michael's actions and proclaims it has been "the worst, most backwards day of my life."
To prevent Oscar from suing the company for anti-gay discrimination, the corporate manager, Jan Levinson, gives him a three-month paid vacation to Europe and use of a company car, a silver Lexus RX 400h, replacing his gold Saturn Ion. (In the Producer's Cut of "The Return" Michael mistakenly refers to the Lexus, a Japanese automobile, as "German engineering".) After going on his vacation with Gil, Oscar returns briefly in "A Benihana Christmas," but decides that it is too soon and leaves before anyone notices him. Oscar finally returns to the office in "The Return" and Michael decides to throw a Mexican themed party for him. Angela, who had acted cold towards him when he came out, apologizes and invites him to be a part of the party planning committee. He is also shown in "Business School" with his roommate Gil at Pam's art show, agreeing with Gil that Pam's art is distasteful.
In "Beach Games", Michael announces that the winner of his Survivor-style game will get his job. In an interview, Oscar states that if Dwight gets the position, he will transfer to Albany. He also mentions that he is trying to get out of his relationship with Gil and (per Angela's suggestion) he might try going out with women for a while.
In "Fun Run", Kevin tries to use Oscar to see if Jim and Pam are dating. In a deleted scene, he says that he was raised Catholic, but now identifies as an agnostic Secular Humanist. In "Money", Oscar helps Michael deal with his financial problems. With Pam and Toby, Oscar is a founding member of the Finer Things Club, which he refers to as the "gayest thing" about him "other than having sex with men".