He's a human Resistance member and the main protagonist of Joutomaa.
Filip was born and bred in the countryside before the Portal Storms began. After losing his family in the aftermath of the "Seven Hour War", he was forced to move into Citizen Containment Zone 19.
Years later, Filip makes the difficult decision to join the Human resistance in order to help smuggle forbidden goods, like clean water and food, into the city and organize the underground resistance. Soon after, he becomes the political prisoner of the Combine.
The mod starts with Valkas in a Citadel mobile cell , where the G-Man appears to him. The story then switches to his rebel story, ending with the G-Man appearing once again and showing him a desolate world, most likely the result of the Combine.