Who is Cyrus Montrose from The Alienist and what is their importance?

Cyrus Montrose is a large black man who works for Dr. Kreizler. Cyrus was once accused in the murder of a police officer. Cyrus worked in a brothel and found the cop taking his graft in trade. Kreizler argued that Cyrus's actions were a delayed reaction to seeing his parents killed by a mob in a riot when he was a small child. Kreizler took Cyrus into his home to save him from a sentence in a public asylum. Cyrus is a loyal employee who does everything Kreizler asks of him, even if it is illegal. Cyrus is injured while helping the investigative team watch the business where they believe the killer will strike again, but he recovers in time to take a minor part in the final confrontation.