- "About two-thirds of your career is locked under a need-to-know seal that requires clearance from ImpSec HQ in Vorbarr Sultana to access. But your publicly recorded awards and decorations appear in a statistically significant pattern following supposedly routine courier missions assigned to you by the Galactic Affairs office. At approximately five times the density of the next most decorated courier in ImpSec history... You were never a bloody courier, Captain Vorkosigan."
- ―Tuomonen is nobody's fool[src]
Captain Tuomonen was the head of ImpSec Serifosa, a small office in Serifosa Dome, Komarr. He was married to a local woman, with whom he had a five-year old daughter, and got along well with the local citizenry.
He was extremely capable, having transformed his intelligence network from a group of unreliable informers into a much better intelligence team. However, due to the quietness of Serifosa, his group was understaffed and unable to track all the Komarran industries. Thus, he was unable to spot troubles brewing among the local Terraforming Project engineers.
Miles Vorkosigan met him while working on the case of the damaged soletta; the two of them became friends. Following the events of Komarr, Miles stated that Tuomonen would have a black mark on his record for failing to uncover the engineers' plot. Miles offered Tuomonen a position as his Auditorial assistant if his career stalled.
The name Tuomonen is Finnish. Possibly the Russian Firsters included some Finns as a subgroup.