Thala-sirens were sizable pinnipeds. These creatures inhabited Ahch-To, a planet, alongside other watery worlds. Recognizable by their extensive flippers, elongated snouts, and udders, these creatures were often observed lounging on the cliffs surrounding the sacred Temple Island. This island was also the location of the first Jedi Temple. Rey encountered them during her journey to find Luke Skywalker, the Jedi Master. These gentle mammals were not targeted by hunters, leading to a lack of fear towards the island's inhabitants. They seemed to enjoy basking in the sun on the island's rocky coastline. The females, referred to as sea sows, produced a nourishing green milk for their offspring. This same milk was also collected by both Luke Skywalker and the native Lanai people, serving as a valuable food source. Their calm disposition meant they were not frightened by individuals like Skywalker when he approached to collect their milk, which became an essential food source during his exile.
During the war between the First Order and the Resistance, green milk from thala-sirens was shipped to Bubo Wamba Family Farms located on the planet of Batuu. There, it was sold at the Milk Stand within Black Spire Outpost. The thala-siren was incorporated as a less common element in the Bubo Wamba Family Farms logo, appearing on their Novelty Drink Vessel.
The thala-siren that Luke Skywalker interacts with in Star Wars: Episode VIII The Last Jedi was a life-size animatronic figure, measuring approximately 18 feet in height. It was designed to integrate seamlessly with the rocks at the filming site, featuring an internal mechanism that allowed its head to tilt forward. Due to its immense size, the puppet required transportation to the location via helicopter. During filming, two puppeteers were positioned inside the puppet: one controlled the shoulders and upper flippers, while the other managed the belly and udder mechanism. An additional five puppeteers were responsible for the head movements, facial expressions, and lower flippers. Two smaller thala-sirens were included as background elements.