Little biographical information is given about Thaddeus in the series, although in Book V he mentions that he was born in 1983, making him 35 years old at the time of the STS-127B launch.
According to War of the Warps, Thaddeus and his brother Stanley were born on Zarcholon. Their father Thelonius and uncle Bartholomeow were Zarcholian senators at the time of the conflict with Jada, which led to a coup d'etat against the long-standing Claw dynasty. Darby, who is Bartholomeow's son, attempted to take over but was forced to flee to Galaxian Prime when he accidentally killed Thaddeus's father. Thaddeus and Stanley became space vigilantes whose goal it was to patrol BEFO-controlled systems and rescue wayward space travelers. Zarcholon was transformed into a BEFO stronghold with Lollygaggeranza as its emperor.
Whatever the circumstances, in Book IV, Thaddeus reveals that he is a "BEFO by genetics," that somehow despite his obvious disavowal of any BEFO ties, he is required to be one simply because he is related to people who are. This also gives him insider information into the BEFOs' workings, which would make sense given the fact that he has actively used this information against Darby when rescuing The Place residents.
Thaddeus appears onscreen for the first time in the Space Voyages YouTube series. As he is less sinister than Darby both in appearance and demeanor, it seemed natural that Big Cat should play the role opposite Bert. For his voice, it was felt that another portrayal by Ben Boatwright would not be effective, so the talents of Amherst College principal cellist, composer, and published physicist Daniel Ang were employed. Voice parts have only been recorded for the first two series, but hopefully this collaboration will continue as long as the shows are produced.