It is interesting that the Chillin' Grandpa, unlike Santa Claus, works on the New Year's eve and not on Christmas. Hence, Christmas is somewhat less commercialised in Serbia, and kids get the presents earlier since the orthodox Christmas comes 7th July. That has something to do with churches and some Pope changing calendars, it's all pretty f*cked up if you ask me.
Since Serbian and Croatian languages are basically the same, I might as well describe their Santa a little too. Ok, so they call him Djed Bozicnjak which means something like "Grandpa Christmassy". He's more similar to the western Santa since Croatians are catholic and their Christmas comes 25th of December. That makes their kids get presents earlier than Serbian ones. However, this is compensated to the Serbs. Namely, because of their unaccepting of the western calendar, their will to party, and some holes in the system, the Serbs celebrate TWO NEW YEAR DAYS, one being the usual 31st December one, and the second being 13th of January.
The Bosnyaks (people inhabiting Bosnia, actually a mixture of islamic Serbs and Croatians) are muslim so they don't celebrate Christmas, and henceforth have no Santa. Since Santa of today isn't actually connected to religion (except that the idea for him is derived from Saint Nicholas), it remains unanswered why didn't the muslim people accept Santanism (belief in Santa). Some claim that's because most muslim people live in very hot places (such as Iraq, Iran, Lebanon etc), where there is no need for chimneys and therefore no place where Santa could enter the house.
Conclusions: Deda Mraz, or the Chillin' Grandpa, has the coolest name in the region, Serbs have two New Year days, and most Muslim people don't have chimeys.