Who is Ostap from Last of the Breed and what is their importance?

Ostap is Kyra's brother-in-law. Kyra asks Ostap for help in finding Mack. After his wife is arrested, however, Ostap locates Mack and uses him to guarantee his wife's release. When Ostap sees how badly Mack has been beaten, he helps him in his escape from Alekhin.