One of the key characters in Arrested Development season 1 was Marta Estrella, but the actress playing her actually changed partway through her run on the sitcom. Arrested Development debuted on FOX back in 2003, telling the story of the formerly wealthy, extremely dysfunctional Bluth family, primarily focused on Jason Bateman's Michael.
While the Bluths all had many reasons to dislike and distrust each other (and sometimes didn’t even need one), one of the biggest in the first season of Arrested Development was Marta’s relationships with Michael (Jason Bateman) and Gob (Will Arnett). She started out in the third episode "Bringing Up Buster" as GOB's girlfriend, a Spanish language soap opera actress. The pair break-up because GOB ignores her, and she later becomes romantically involved with Michael.
When she was first introduced, Marta was played by Leonor Varela, who appeared in the aforementioned third episode and Marta's second installment, "Key Decisions". However, since filming she’d taken on a role in the film Voces Inocentes, and so had to drop out of the role because of scheduling conflicts. From the seventh episode of Arrested Development season 1 onwards, Marta was instead played by Patricia Velasquez, who continued in the role for a further four appearances, culminating in her final episode "Beef Consomme". The change worked with the show's humor though, as it fit with how soap operas operate, making it a fun meta-touch too.
Since leaving Arrested Development, Varela has mostly worked in Spanish language films, although she has appeared on U.S. TV since, with credits in both Agents of SHIELD and Lethal Weapon. Valasquez, meanwhile, has similarly appeared in a number of Spanish movies, and most recently had a part in The Curse of La Llorona.
Despite the very meta nature of Arrested Development, no one on the series seemed to notice or acknowledge the change. Fans, however, did realize, and have come up with a way of differentiating them. A’s character is referred to as Marta 1.0, and then B’s version is known as Marta 2.0, much like Arrested Development's long-running Lucille/Lucille 2 gag.
Marta eventually left both Bluth brothers after witnessing them - and Buster - all fighting over her, because to her family was the most important thing in the world. It might've served as a momentary wake-up call for Gob and Michael, but it wasn’t long before they were fighting again. Although subsequent seasons - including Netflix's Arrested Development revival - would cover similar ground with GOB and Michael’s love interests, Marta herself never officially returned after season 1. However, in season 3's "Forget-Me-Now", another Marta - dubbed Marta 3.0 - is introduced as woman Michael once-dated. The writers decided to do this in post-production to continue the running Marta joke, but it's unlikely this is the same Marta as the previous two.