Born: Arvidsjaur, Sweden
Voice actor: Peter Stormare
Since he was born Mattias has been seeking the most exciting and intense experience he could find. When he was young he joined Sweden’s Arctic Rangers. But when he was discharged for insubordination, he joined the motorcycle gang called the Wolfpack Brotherhood. With the help of Mattias the gang grew to be the most wanted criminals in Sweden and Mattias was thrown in jail. After he escaped he was no longer allowed to return to Sweden and became a mercenary for the large income, the exciting lifestyle and a job that took him all over the world.
In the first game Nilsson had only been with Ex-Ops for one year, a relatively inexperienced operative compared to the other two characters. He can speak English, Swedish and Russian, the latter allowing him to understand conversations Sergei (Russian mob leader) and Josef (Sergeis' assisant) have with each other.
He is the youngest Mercenary at 33 years of age. He is the fastest Mercenary, however his appearance makes him stand out more so he is easily spotted by enemies.
"Long way down! WOO!"
"Chicks dig scars. And shrapnel."
"I'm not much of a `gadget guy.`"
"M67s. I love M67s."
"Isn't this what fuel air bombs are for?"
"I love APCs! So crunchy!"
"I think I like Colonel Peng. Even the stick up his butt has a stick up its butt."