Captain Chenkov of Valhalla

Any Imperial Guard unit within 12" of this model may take Break tests using their Leadership value

Allowed re-rolls for any Leadership based tests (break, psychology, rally, etc.). 
At the start of the game the Imperial Guard player rolls a D6. That score is the number of re-rolls he is permitted during the game. These can be used any time as long as Chenkov is still alive.

As long as Chenkov is still alive, one reroll is added every time the enemy receives victory points for wiping out or breaking a unit. Note that no bonus is earned for reducing a unit to half strength, only for wiping it out or breaking it.