Maybe his parents were admirers of Al Smith, the happy warrior...who was a 'Rat, after all.
"Ratko" means "Warrior".
Not a surprising name. The 20th Century saw a lot of wars in the Balkans-- The Balkan Wars, WWI, WWII, and eventually the break up of Yugoslavia. Every single generation of Serbs for the last 500 years has had to give up some men to kicking some empire's or country's designs for the Balkans to the curb. Between the Balkan wars and WWI, Serbs lost nearly 50% of their young manhood to defending their land.