Character: Laslo Ković
Game: Battlefield 4
Summary: Agent Laszlo "Whistler" Kovic is a CIA agent featured in Battlefield 3 and Battlefield 4. It was stated he fought in the Bosnian War according to the cutscene before Kaffarov where he got his friends killed by a rocket attack due to them not being warned about it by their sentry, who was sleeping at the time...
More info: Battlefield.wikia.com
A few reasons why some think he may be a Serb:
1. Last name: Kovic, or Serbian - Ković; but he also may be Hungarian, as his first name, Lazlo, is Hungarian. Also, a variation of his last name, Kovacz, is also Hungarian.
2. Involvement in Bosnian Conflict - if possible, one army, who has intention to attack any country, will deploy, if possible, a number of men/women who are associated or have any kind of connection/knowledge about the people, cities, places, culture and heritage of the "attacked" country, on it's soil (intelligence purposes). That's a case with Kovic.
Interesting points
Настави са добрим радом -HawkEye- ,ти си тај који држи ову групу живом.