Late Middle Ages
In 1338, the Assassins saved Lukas Zurburg from a thief on the road to Adendorf and subsequently recruited him into the order. In 1348, the plague swept across Essen, wiping out nearly half of the town's population. From there, a group called the Brothers of the Cross, a Templar organization, began promising protection from the plague.
Working with the Italian Brotherhood
Prior to 1502, a historian named Conradus Celtis had spent years uncovering the secrets of history. Having discovered even the history of the Assassins, he came to admire them and sought to compile a comprehensive text that honored them as heroes. Despite this, the Assassins recognized the grave dangers in exposing their order to the public, and sometime around 1501 to 1502, a team of Italian Assassins visited him in Cologne, Germany to ensure that he agreed to keep their existence hidden to common society, and took his works back to Rome.
In 1502, the Elector Friedrich der Weise planned to open a university in Wittenberg, which challenged the practices of the Borgia Papacy and promoted religious reform. In response, Pope Alexander VI, Grand Master of the Roman Rite of the Templar Order, sent a bribe to convince him to back away from the "foolish project", though the Assassins intercepted the money and used it to give him a large, anonymous donation.
The Holy Roman Emperor, Maximilian, had taken a heavy beating from Swiss mercenaries during the Swabian War, to which the Borgia had hired several of these commanders as their Papal Guard. Drinking with these mercenaries at a tavern, the Assassins slipped poison into their drinks, before carrying them out. Under the guise of condottieri, they delivered the commanders to Maximilian, to which the Emperor used them to train an army of his own, in order to rival the Swiss.
Following this, he invited the Assassins to help the Swiss train the army, as they had previously bested the Swiss. Once again disguised as condottieri, they helped him train the first of the "Landsknechte", upon which he offered them a regiment should they ever need one.
World War II
During World War II, the Assassins discovered that Adolf Hitler was in possession of an Apple of Eden, given to him by the Templars, which he had used to form Nazi Germany and hypnotize the population to join his cause and start the war. On 30 April, 1945, Hitler executed his double inside the Führerbunker and was supposed to flee and meet up with Winston Churchill. However, the Assassins were watching the bunker and killed Hitler when he stepped outside; presumably taking the Apple for themselves.
Allies and puppets