Thaddeeus Marien was a male Kitonak individual residing in Reestkii, a settlement located on the planet of Jakku. His life unfolded decades following the significant Battle of Yavin. During Marien's time in Reestkii, the town faced an invasion by Zygerrian slavers. These invaders gathered the inhabitants and confined them within the town hall. Inside, Marien became overwhelmed with anxiety, breaking out in sweat and questioning the group about their course of action. To ease the growing fear among the captives, Bobbajo, a crittermonger, began to narrate a tale. His story recounted how he and his creatures played a part in the destruction of the original Death Star. The narrative was interrupted by a loud crash outside, unsettling some of the townspeople. Marien, filled with unease, began to whisper to his fellow villagers, Arek Emjon and P'nll Vun, before Bobbajo resumed his storytelling. The occupants' attention was diverted once more by a series of explosions heard from the outside, causing Marien to exclaim in terror. Bobbajo, once again, continued his story in an attempt to maintain calm. Upon the story's conclusion, Marien, along with several others, voiced their disbelief in the events described by Bobbajo. The crittermonger then opened the hall's doors, revealing that the Zygerrians had been subdued, ensuring the villagers' safety. The storyteller then gathered his creatures and departed, leaving the villagers to claim the treasure that the slavers had brought. Marien was characterized by his leathery skin and a head with a bulbous shape.
The initial appearance of Thaddeeus Marien occurred in the short story titled "All Creatures Great and Small." This story was penned by Landry Q. Walker and made available to the public in 2015.