He's a police officer with the ZPD. For years after becoming an officer, he hid the fact that he was gay, but word got out. It was in the locker room, and Mackenzie was packing up to go home for the evening. His personal diary fell out of his locker, and either Wolford or Fangmire grabbed it before he could pick it up. They read through it and found an entry in which he wrote about coming out of the closet about his orientation. Whistler tried to grab his diary back from them, but they held it out of his reach, and proceeded to toss it around the locker room to a couple other officers, who also saw Whistler's diary entry. When Mackenzie returned to work the next day, word was slowly spreading through the police station. Since that day, he has been treated differently. Other officers don't talk to him as much, they're wary of him in the locker room, he's often slandered (usually during breaks or behind closed doors), his pay was reduced, and someone once keyed his car with the word "Fleabag" (Zootopia's equivalent of f*g).

And also he was shot with the nighthowler serum during the "savage predator scare". He called in a 10-00 (officer down - all patrols respond), but the officers who did respond took their own sweet time. Same with calling an ambulance once they were on the scene. After the ambulance arrive, Whistler was rushed to the hospital and given a dose of nighthowler antidote, later making a full recovery and returning to work. He's still treated the same.

Personality: Both at work and in public, he may seem cold, bitter, jaded, and anti-social, but it's just a façade; in truth, he's hiding intense feelings of sadness, anger, and loneliness. Don't get me wrong, he loves his job, it's just that he's tired of being treated differently because of his orientation.

Age: Late 30s

Voice actor: Paul Brandt - https://www.youtube.com/watch?v=7GOscHRPC-k