Itinerant bunch of nomadic tribesmen who got pushed west from their ancestral grazing lands by someone harder than they were (probably the Mongols).
Moved in and slapped the struggling Byzantine empire about at Manzikert in 1071ish. Still took the lazy sods till 1453 to capture Constantinople. (note: if a bloke comes to your door selling big guns, DONT send him to your aggressive next door neighbour who has always fancied your patio!)
Promptly moved into the Balkans and started sowing the seeds for the situation that resulted in the racial cleansing we are so familiar with today. Ruled the entire eastern end of the Med for 350 years although they were given a run for their money By the Kights of Saint John (Hospitallers). Reached their high point when they conquered all the way to Vienna before the Holy Roman Empire gave then a complete and total shoeing outside the city walls.
Noted for their almost unstoppable elite troops - the Janissaries (christians converted to islam as children). The Viennese found a way to deal with these suicidal knutters - kill the first ones over the wall, wrap the body in a pig skin then toss the stiff back over the walls and into a ditch. Volunteers to charge the walls started to dry up. According to islam it stops them getting to heaven and the 72 virgins. Really think the Viennese might have had something there!
Today the only secular Muslim government in the world is Turkish and thus the only Muslim state not on the edge of Jihad, falling apart or currently threatening to nuke our kaffir arrses. Although for how much longer this friendly Islamic country will remain secular, no-one can say.