The roman letter Q is used to denote a sound which in fact is not found in any European language, and so far as I know Arabic is unique in possessing it. Our letters G and K are formed by creating a constriction in the mouth. The base of the tongue is moved to meet the roof of the mouth to completely block the airflow, then a sudden unblocking forms either of these sounds, depending on the amount of pressure we create behind the blockage before releasing.
The arabic sound on the other hand is created by blocking the airflow at the top of the windpipe (i.e. further back and down) and then releasing. The sound created by this is very distinctive and unless you have been brought up with it from infancy it is very difficult to imitate. Arabs and some other nationalities, who have learned it through arabic connections through Islam, also master it fairly well. Native Arabic speakers clearly hear the difference when the rest of us speak Arabic without the true "Q", however fluent we are. There is something of an analogy in the two types of "R" found in European languages (German/Dutch/ French, versus say the Spanish/Italian/Nordic (except Danish).
The closest most of us get to prouncing the name correctly is Gattar (not gaTTAR - the correct emphasis is on the first syllable).