Assassins or Hashashins !

The Assassins' library was destroyed when their fortress fell, so we do not have any original sources on their history from their own perspective. Most of what survives comes from their enemies, or from fanciful second- or third-hand European accounts.

However, we know that the Assassins were a branch of the Ismaili (recognize six Imams) sect of Shia Islam (who normally recognize the 12 Imams). The founder of the Assassins was a Nizari Ismaili missionary called Hassan Sabbah, who infiltrated the castle at Alamut with his followers, and bloodlessly ousted the resident king of Daylam in 1090. From this mountaintop fortress, Sabbah and his faithful followers established a network of strongholds and challenged the ruling Saljuk Turks, Sunni Muslims who controlled Persia at the time.

The name Assassin diverts from the Egyptian term of Hashishin which itself means troublemakers; all other terminologies and definitions are wrong and has nothing to do with any drugs or other wrongly believed nonsense whatsoever. The modus operandi was always the same, in order to get rid of anti-Nizari rulers, clerics and officials, the Assassins would carefully study the languages and cultures of their targets. An operative would then infiltrate the court or inner circle of the intended victim, sometimes serving for years as an advisor or servant. At an opportune moment, the Assassin would stab the Sultan/King, minister, or cleric with a dagger in a surprise attack. Assassins were promised a place in Paradise following their martyrdom, which generally took place shortly after the attack. Officials throughout the Middle East were terrified of these surprise attacks; many took to wearing armor or chain-mail shirts under their clothes, just in case.
For the most part, the Assassins' victims were Saljuk Turks or their allies. 

The first and one of the best-known was Nezam ol-Mulk, a Persian who served as vizier to the Saljuk court. He was killed in October of 1092 by an Assassin disguised as a Sufi mystic. A Sunni Caliph, Mustarshid, fell to Assassin daggers in 1131 during a succession dispute. In 1213, the sharif of the holy city of Mecca lost his cousin to an Assassin. He was particularly upset about the attack because this cousin closely resembled him. Convinced that he was the real target, he took all Persian and Syrian pilgrims’ hostage until a rich lady from Alamut paid their ransom.

Why did the Assassins attack the Saljuks? As Shi'ites, many Persians had long felt mistreated by the Arabic Sunni Muslims who controlled the Caliphate for centuries. When the power of the caliphs faltered in the 10th-11th centuries, and Christian Crusaders began to harry them in the eastern Mediterranean, the Shi'a thought their moment had come. However, a new menace arose to the east, in the form of the newly-converted Turks. Fervent in their beliefs, and militarily powerful, the Sunni Saljuks took control of a vast region including Persia. Outnumbered, the Nizari Shi'a could not defeat them in open battle. From a series of mountaintop fortresses in Persia and Syria, however, they could assassinate Saljuk leaders - and strike fear into their allies.

In 1219, the ruler of Kharazm, in what is now Uzbekistan, made a huge mistake. He had a group of Mongol traders murdered in his city.  Changiz Khan was furious at this affront, and led his army into Central Asia to punish Kharazm. Prudently, the leader of the Assassins pledged loyalty to the Mongols at that time.
By 1237, the Mongols had conquered most of Central Asia. All of Persia had fallen except for the strongholds of the Assassins - perhaps as many as 100 mountain fortresses. The Assassins had enjoyed a relatively free hand in the region between the Mongols' 1219 conquest of Kharazm and the 1250s. The Mongols were focusing elsewhere, and ruled lightly. However, Changhis Khan's grandson Mongke Khan grew determined to conquer the Islamic lands by taking Baghdad, seat of the caliphate. Fearful of this renewed interest in his region, the Assassin leader sent a team to kill Mongke. They were supposed to pretend to offer submission to the Mongol khan, and then stab him. Mongke's guards suspected treachery and turned the Assassins away, but the damage was done. Mongke was determined to end the threat of the Assassins once and for all. (not a proven fact, but largely presumed to have been the motivation).

Mongke Khan's brother Hulagu set out to besiege the Assassins in their primary fortress at Alamut. (in the meantime, the sect leader who ordered the attack on Mongke had been killed by his own followers for drunkenness, and his rather useless son now held power). The Mongols threw all of their military might against Alamut, while also offering clemency if the Assassin leader would surrender. On November 19, 1256, he did so. Hulagu paraded the captured leader in front of all the remaining strongholds, and one by one they capitulated. The Mongols tore down the castles at Alamut and other places, so that the Assassins could not take refuge and regroup there. The following year, the former Assassin leader (now on the run) asked permission to travel to Karakoram, the Mongol capital, in order to offer his submission to Mongke Khan in person. After the arduous journey, he arrived but was denied an audience. Instead, he and his followers were taken out into the surrounding mountains and killed. It was the end of the Assassins.
  
Looking carefully at history, structure and tactics of the original Assassins, you cannot help but stumble on the fact that today we seem to have an identical organization in our Modern World, doing exactly the same. Infiltrating, spying, manipulating and finally assassinating its rivals and its enemies. This organization is called “The Mossad of Israel”. (Look at all the murders of Iranian scientists amongst others).  Let’s hope their end, is also the same as their role models. (Thanks to K.Szczepanski).