After the actions at Hagia he became the second commissar of the Tanith regiment, dealing more with the day to day commissariat duties while Colonel-Commissar Ibram Gaunt dealt with the command duties of running the regiment.
When Ibram Gaunt went on the mission to Gereon Hark was the head Commissar for the Tanith. But during the time between Gaunt's mission on Gereon and his return the Tanith First had been mixed with the Belladon 81st Recon Regiment and became the 81st/1st Recon. After the campaign during "His Last Command", the Tanith First was reformed and was back under the command of Gaunt, with Hark returning to his role as the chief political commissar while Gaunt commanded the regiment.
Viktor Hark is known to have used a Plasma Pistol.