During the recent decade, the most loyal allies of Russia have been Iran, Iraq, and the official government of Syria.
These countries, including Assad-controlled territories of Syria, all have been also known as primarily populated by Muslims who belong to Shia denomination of Islam.
In the earlier times, however, Russia did support regimes in countries who are also Sunni, but this does not seem to be the case at the moment.
My question was inspired by a friend of mine who told me something like "Putin together with Shiites is fighting against Sunnites". Despite this may be a too bold statement, the question is:
Why are the most loyal allies of the Russia are Shiites?
"It's just a coincidence" may be also a good answer if backed with some credible explanation or historic/economic/religious reference.