The Salafis are a very broad, amorphous grouping of Muslims who believe that the only way to salvation is to follow, strictly and fully, the way of life of the earliest Muslims (whom they revere as the "Salaf us Saleh", or "Righteous Predecessors", the 'Puritans' of the Muslim collective, if you like). Although they would like to present themselves to other Muslims as belonging to a timeless tradition, Salafism in fact can be traced to around the time of the collapse of the Crusader states, when a Damascene Islamist preacher, Ibn Taymia (1263-1328) began to preach a puritan, unornamented form of Islam which had little or no foreign innovations ("bid'a"). For most of history, the Salafis spurned modern political formations, putting them at odds with, amongst others, the Muslim Brotherhood. Although Ibn Taymia's teachings did not spread too far at the time, it did, centuries later, give birth to the rise of Wahhabism in what was to become Saudi Arabia.
Both Salafia and their subset, the Wahhabis, had little or no time for temporal politics for a very long time, before a young man in the Kingdom of Saudi Arabia sought to remake his country in the Salafi-Wahhabi mould. Not all Salafis look the same, and the guys above are a fashionable rogues gallery of exceptional Salafis.