Who is Stevie Taggert from The Alienist and what is their importance?

Stevie Taggert is an employee of Kreizler. Stevie was once a street urchin who was arrested for theft. In juvenile hall, Stevie was abused by a guard in a sexual manner. Stevie stabbed the guard, wounding him. Kreizler testified at Stevie's trial, convincing the judge to allow the boy to move into Kreizler's custody rather than return to jail. Stevie becomes a lively part of the investigation into the boy-prostitute killings, often escorting the team members to various locations and bumming cigarettes any time he can.