What does Zaroff explain to Rainsford about Ivan? What is Ivan's backround?

Apperently Ivan is "deaf and dumb". Ivan is a Cossack like Zaroff.

Here is the quote should you need it,

"Ivan is an incredibly strong fellow," remarked the general, "but he has the misfortune to be deaf and dumb. A simple fellow, but, I'm afraid, like all his race, a bit of a savage."

"Is he Russian?"

"He is a Cossack," said the general, and his smile showed red lips and pointed teeth. "So am I."

Ivan was a Russian Cossack, a military specialist who'd fought who as a mercenary soldier in service to the czar until the collapse of the Russian empire in 1917. He is Zaroff’s mute assistant; a large man with a waist-length black beard; he wears a black uniform. He is known to be a vicious torturer, someone who tortures his victims to death.

Zaroff explains to Rainsford that those who do not comply with his desire to hunt them have the alternative of being turned over to Ivan.