The game Assassins creed is based on Ismaili shias the assassins. Who were they?

The game Assassins creed is based on Ismaili shias the assassins. Who were they?
Ibn Battuta mentioned.
ثم بحصن الكهف. وهذه الحصون لطائفة يقال لهم: الإسماعيلية، ويقال لهم الفداوية. ولا يدخل عليهم أحد من غيرهم. وهم سهام الملك الناصر، بهم يصيب من يعدو عنه من أعدائه بالعراق وغيرها، ولهم المرتبات. وإذا أراد السلطان أن يبعث أحدهم إلى اغتيال عدو له أعطاه ديته، فإن سلم بعد تأتي ما يراد منه فهي له، وإن أصيب فهي لولده. ولهم سكاكين مسمومة يضربون بها من بعثوا إلى قتله. وربما لم تصح حيلهم فقتلوا.
Then I went to The castle al Kahf, al Ismaeeliya have all these castles, they are also called Fidaiyah (In medieval Iran, Syria, and Lebanon, a member of a secret organization of assassins.). No one can enter these (castles) other than them.
They are like the arrows of Malik Nasir. Wherever there is any enemy of Malik Nasir they attack them. There are wazaaif for all of them in the court of King. When the King wants to kill any of his enemy he makes one of them agree to it and give him specific amount if he comes back alive otherwise if he dies the amount is given to his children or family.
They (the Assassins) always have poisoned daggers, they kill the appointed person with it sometimes they themselves get killed.
(al Rihla Ibn Battuta part 1)
P.S I have never played this game just saw the videos of it and read about it. Looks good though.