Star Trek: The Original Series episode "Balance Of Terror," where Captain James T. Kirk and a Romulan captain play a deadly game of cat and mouse in space. The Romulans have maintained a presence in virtually every Star Trek series since, though usually from a distance, maintaining their inherent mystery.
The deepest dive yet into Romulan culture and society came in the first season of Star Trek: Picard. Though somewhat blunted by the destruction of their home world Romulus by a supernova - technically set up in the 2009 J.J. Abrams Star Trek in the Kelvin timeline - the Romulans remain a serious threat to the Federation, having even covertly infiltrated Starfleet. However, rather than their usual fascistic quest for power, Star Trek: Picard featured a subset of Romulans motivated by a prophecy that artificial life will lead to the end of the universe, an entirely new angle on the pointy-eared scoundrels.
What Star Trek Showed About Romulans Hating Androids Before Picard
Star Trek: Picard establishes that the Romulans' artificial life hatred is fueled by the Zhat Vash, a top secret division of the Tal Shiar, essentially the Romulan Secret Police. The Tal Shiar have a long and storied history in Star Trek, but there's never really been any indication that they had a problem with artificial life. The closest hint of this was in the the android Lietuenant Commander Data he knows plenty of Romulan cyberneticists who would love to get their hands on the Enterprise's stalwart second officer.
Data's other major encounter with the Romulans came in the two-part episode "Unification," where he and Captain Jean-Luc Picard covertly visit Romulus in an effort to find Spock, who they fear may have defected. In actuality Spock was fueling a revolution on Romulus in an effort to reunify the sibling Vulcan and Romulan races. Neither the rebels nor the more nefarious Romulans like Sela seem particularly wary of Data, with Sela even itting a begrudging respect for the android.
How Else Picard Season 1 Retconned The Romulans
The obsessive hatred of artificial life isn't the only new aspect of Romulan society introduced in Star Trek: Picard. The show also introduced the Qowat Milat, an organization of warrior nuns who helped Starfleet in their efforts to relocate the Romulan population when it became clear Romulus was doomed. The Qowat Milat raised the orphan boy Elnor, who would go on to become part of Picard's La Sirena crew and the first full-blooded Romulan itted to Starfleet Academy.
Perhaps most consequently, the show built a deep spiritual mythology for the Romulans, who had previously been portrayed as a fairly agnostic race. That newfound spirituality found benevolent ends in some corners of Romulan society, like Star Trek: Picard's Romulan sect the Qowat Milat, but it also fueled the paranoia and distrust of artificial life that nearly resulted in genocide. Star Trek: Picard is likely done with the Romulans at this point, as it's navigating a decidedly different path in its third and final season, but the Romulans figure to continue evolving and thriving in the years to come.