Warning: SPOILERS for Star Trek: Picard Season 2, Episode 1 - "The Star Gazer"
The Deltans return in Star Trek: Picard season 2 after originally being introduced in Star Trek: The Motion Picture. A year and a half after the ending of Star Trek: Picard season 1, Admiral Jean-Luc Picard (Patrick Stewart) now confronts questions about his lifelong choices as he's called upon to confront an incursion by the Borg and a new, alternate timeline created by Q (John de Lancie). But Picard's motley crew also find themselves at new stages in their lives, and this includes Soji (Isa Briones), who establishes contact with the Deltans in the Beta Quadrant.
The most famous Deltan in Star Trek was Lt. Ilia (Persis Khambatta), who was the navigator of the USS Enterprise in Star Trek: The Motion Picture. Like all Deltans, Ilia was bald and strikingly attractive. She was also the love interest of Captain Will Decker (Stephen Collins), who had a romantic past with Ilia years before they served on the Enterprise during the mission to stop V'Ger from reaching Earth. Ilia and the Deltans were originally created for the Star Trek Phase II TV series that was eventually turned into Star Trek: The Motion Picture by Paramount following the blockbuster success of Star Wars in 1977. Along with being bald, Deltans are known for being extremely sexually attractive. As such, Deltans like Ilia swore an oath of celibacy when they joined Starfleet.
The Deltan homeworld is Delta IV in the Alpha Quadrant but in Star Trek: Picard season 2's premiere, "The Star Gazer," Soji met with a delegation of Deltans in the Beta Quadrant world of Raritan IV. Now a free citizen of the United Federation of Planets after the ban on synthetics was lifted, Soji has become an ambassador for her race of androids built from the deceased Commander Data (Brent Spiner) who live on the planet Coppelius. Also present was Dr. Agnes Jurati (Alison Pill), who, as a human, was notably suffering from the effects of close contact with the alluring Deltans. A Deltan male even tried to charm Jurati by asking to see the "hands that built" the synthetic wonder that is Soji. However, Agnes was already reeling from her rocky relationship issues with the USS Stargazer's new Captain, Cristobal Rios (Santiago Cabrera), and she quickly beamed aboard the starship, leaving Soji behind with the Deltans on Raritan IV.
After Lt. Ilia and Captain Decker merged with V'Ger and left their plane of existence at the end of Star Trek: The Motion Picture, other Deltans made a few canonical appearances in Star Trek. There was a Deltan serving on the USS Excelsior in Star Trek III: The Search For Spock and Deltan ambassadors appeared in Star Trek IV: The Voyage Home and Star Trek VI: The Undiscovered Country. On Star Trek: Enterprise, Ensign Travis Mayweather (Anthony Montgomery) also told a story of his encounter with Deltans when he was a teenager. However, there have been no major Deltan characters in Star Trek since Lt. Ilia.
When Gene Roddenberry created Star Trek: The Next Generation, he repurposed the initial concepts for the Deltans, Ilia, and Will Decker into the Betazoids, Counselor Deanna Troi (Marina Sirtis), and Commander Will Riker (Jonathan Frakes). Riker and Troi had a past romance like Decker and Ilia, and the Betazoids had a sexy component like the Deltans since they were known for marriage ceremonies in the nude. It's unclear whether the Deltans will play a larger role in Star Trek: Picard season 2 but the bald aliens continue to thrive in the early 25th century.
Star Trek: Picard Season 2 streams Thursdays on Paramount+.