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

Cyrus Montrose is a large black man who is employed by Dr. Kreizler. He was once accused of murdering a police officer when he worked in a house of prostition and caught 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 and took Cyrus into his home to save him from a sentence in a public asylum.