WARNING: SPOILERS for Star Trek: Picard season 3, episode 3- "Seventeen Seconds"
While he's never made an actual physical appearance in Star Trek: Picard, the late Thad Riker remains a crucial story point for his grieving parents, William Riker (Jonathan Frakes) and Deanna Troi (Marina Sirtis). Thaddeus Riker was born on the USS Titan in 2381, two years after Riker took command of the ship at the end of Star Trek: Nemesis. Thad also has a younger sister, Kestra (Lulu Wilson). Thad became ill with a rare disease, prompting the Riker family to effectively retire from active Starfleet duty and relocate to the restorative planet Nepenthe. Despite their efforts, Thad succumbed to his illness as a teenager.
The Riker family remained on Nepenthe, where they provided refuge for Jean-Luc Picard (Patrick Stewart) and Lieutenant Commander Data's (Brent Spiner) android offspring Soji (Isa Briones) in Star Trek: Picard season 1. The lone appearance by Thad Riker was a photo of the infant Thad with Picard seen in the Rikers' home. While Riker and Troi were clearly happy to see Picard and were more than willing to help him on his mission, they were still clearly mourning Thad. Their grief has endured into Picard season 3, with Riker clearly affected by Picard meeting his previously concealed adult son, Jack Crusher (Ed Speleers).
