Santana Lopez is a fictional character from the Fox musical comedy-drama series Glee. The character was portrayed by Naya Rivera, and appeared in Glee from its pilot episode, first broadcast on May 19, 2009. Santana was developed by Glee creators Ryan Murphy, Brad Falchuk, and Ian Brennan. Introduced as a minor antagonist and a sidekick to Quinn Fabray (Dianna Agron) in the first episode of Glee, Santana's role grew over the course of the show's first season. In the second season, Rivera was promoted to a series regular, and Santana was given more high-profile storylines, such as the development of her romantic feelings for her best friend Brittany Pierce (Heather Morris), and the subsequent realization that she is a lesbian. Rivera, who was vocally supportive of the love story between her and Morris' character, received widespread praise for her portrayal of Santana, as well as for her for vocal work in numerous songs performed as part of the show's central glee club, New Directions.

Santana is introduced alongside Quinn and Brittany as one of the three most popular cheerleaders at the fictional William McKinley High School in Lima, Ohio, where the show is set. She joins the school's glee club, and soon is spying on it for Sue Sylvester (Jane Lynch), coach of the cheerleading team the Cheerios. As the season progresses, she becomes more sympathetic to other glee club members, saying she is staying in the club not because Sue is forcing her, but because she likes it.

She has several romantic relationships, briefly dating Noah "Puck" Puckerman (Mark Salling), taking Finn Hudson's (Cory Monteith) virginity, and carrying on a friends with benefits relationship with Brittany. In season two, the show delves into the motivations behind Santana's antagonism and her sexual aggressiveness towards boys; it is later revealed that her cruel attitude is partly driven by her struggle with her romantic feelings towards Brittany, and subsequently with her lesbian identity. This storyline was positively received by critics.

Santana is introduced as a popular cheerleader at William McKinley High School. Santana and her friends, cheerleaders Quinn Fabray and Brittany Pierce, join the school glee club, New Directions, because Quinn wants to keep an eye on her boyfriend Finn Hudson; cheerleading coach Sue Sylvester then enlists the three of them to help her destroy the glee club from the inside. Initially romantically linked to football player Puck, Santana soon breaks up with him over his bad credit score, though the two have an on-again, off-again relationship well into the show's second season. Brittany also reveals in an offhand comment that she and Santana have slept together. When the two are accused of giving Sue the New Directions set list for their first show choir competition, Santana defends herself and admits that she has come to enjoy participating in the club. After Quinn is kicked off the cheerleading squad due to her pregnancy, Santana takes over as head cheerleader. At Sue's behest, Santana and Brittany go on a date with Finn, who is now the glee club co-captain. Santana takes his virginity, though Finn immediately regrets sleeping with her. When Puck briefly dates Mercedes Jones (Amber Riley), Santana is jealous and confronts her with an aggressive duet of "The Boy Is Mine". A similar confrontation, though entirely physical, occurs in the second season after Puck sings a love song to Lauren Zizes (Ashley Fink) in front of the glee club, though Santana loses badly to Lauren.

Santana is demoted from her position as head cheerleader when Quinn reveals that she had breast implants over the summer, leading to a physical fight between the two. While making out, Brittany suggests to Santana that the two of them should sing Melissa Etheridge's "Come To My Window" for a glee club duet competition. Alarmed, Santana claims that she was only sleeping with Brittany because Puck was temporarily unavailable. Brittany begins to date club member Artie Abrams (Kevin McHale), which piques Santana's jealousy. She briefly quits the glee club with Brittany and Quinn when Sue demands that they choose between being in glee club and being cheerleaders, but Finn convinces them to reverse their decision, and they quit the Cheerios instead. Temporarily without a boyfriend after Puck begins dating Lauren, she breaks up Quinn and her boyfriend Sam Evans (Chord Overstreet), and dates him herself for several weeks. Confronted by Brittany about her feelings for her, Santana confesses that she is in love with her but fears being ostracized by the student body for being in a same-sex relationship, due to what had happened to Kurt (Chris Colfer), who is openly gay, so many times that year. Brittany says she reciprocates her love, but as she also loves Artie, she will not break up with him. In the hope of convincing Brittany to drop Artie and be with her, Santana runs for school prom queen. She blackmails closeted jock and Kurt's bully Dave Karofsky (Max Adler) into becoming her beard and running mate, and to also start an anti-bullying campaign with her to get Kurt to transfer back, as he only left McKinley to go to Dalton Academy for a safe school environment because Karofsky had threatened to kill him. He wins prom king, but Santana is not named queen; instead, it is Kurt. Brittany comforts her, and encourages her to embrace her true identity.

In season three, Santana and Brittany rejoin the Cheerios, and Sue appoints Santana co-captain along with Becky Jackson (Lauren Potter). Santana is briefly banished from New Directions for disloyalty, and though she is soon allowed to return, she leaves again to join Mercedes in a newly formed all-girl glee club, the Troubletones, and convinces Brittany, who is now her girlfriend, to come with her.

In "Mash Off", Santana pushes the growing rivalry between the clubs to a new level by bullying Finn and Rory. When her supposed apology to Finn becomes another stream of insults, he accuses her of being a coward for tearing other people down because she can't admit that she's in love with Brittany, thus outing her in a crowded public hallway. They are overheard, and Santana's now-revealed lesbianism is used in an "attack" ad against Sue by one of her opponents in the congressional election campaign. Though Santana is warned before the ad runs, she is nevertheless devastated by being publicly outed: she hadn't yet come out to her family. She does so, and while her parents accept her declaration, her grandmother is offended that Santana has made her sexuality public and disowns her, leaving Santana heartbroken. After slapping Finn for outing her, she was almost suspended and made to apologize, while Finn received no repercussions for the outing which caused the slap.

The Troubletones are defeated by New Directions at Sectionals, and Quinn convinces Santana, Brittany and Mercedes to return to the New Directions, having arranged for them to be guaranteed one Troubletones number in all future competitions. When Principal Figgins tells Santana and Brittany in "Heart" to stop kissing publicly at school because he's received complaints, despite not enforcing the same ban on heterosexual couples, Santana is angry, and uses the God Squad's singing-valentine fundraiser to make a point by hiring them to deliver a love song valentine to Brittany.