NBC's "Chicago Fire" follows the personal and professional lives of a group of first responders at a Chicago firehouse. Its popularity is owed to the cast and authenticity.

"Chicago Fire" is dedicated to showing firefighters as realistically as possible. Series regular David Eigenberg brings realism to his role via his real-life military experience.

Eigenberg plays one of the most beloved characters, Lieutenant Christopher Herrmann, as he mentors the greener employees of Firehouse 51 alongside other veteran firefighters.

The actor joined the cast in the first season, but long before acting as a fictional firefighter, he devoted many of his early years to the Marines.

He has partnered with the United Service Organization (USO), a charity that provides live entertainment, social connection, and resources to the United States Armed Forces.

On a 2019 USO tour, he went out of his way to offer a special "thank you" to the fire department, saying,

"[firefighters] understand that you understand the service."