Thalen was a Xindi-Primate engineer assisting Degra in building the Xindi weapon. He was Degra's friend and chief confidant.
In 2154, Thalen assisted Degra in testing the second prototype of the Xindi weapon in the Calindra system. Their work was interrupted when the Andorian warship Kumari stole the prototype, which was later destroyed by Captain Archer of the Enterprise. (ENT: "Proving Ground") Shortly thereafter, Thalen was captured along with Degra by Archer and the crew of Enterprise to gain information as to the whereabouts of the weapon. His voice was duplicated in an attempt to trick Degra into revealing the coordinates of the Azati Prime system. His memory was erased by Phlox so he would not remember the incident, or that Degra had unknowingly revealed the location of the weapon. (ENT: "Stratagem")
Later, in February 2154, as Degra's ship returned to Azati Prime, Thalen shared a toast with Degra over the near-completion of the weapon. (ENT: "Azati Prime")