- "Trust is a dangerous trait, Hamid."
- ―Arbaaz Mir to his Mentor, 1839.[src]
- "Your people in Kashmir suffered a great tragedy, my friend. But those days have long passed and Singh's strength is all that stands between India and the growing British power."
- ―Hamid to Arbaaz, about Singh's actions, 1839.[src]
Arbaaz Mir was born in Kashmir in northwestern India during the early 19th century to a Muslim family. His home region was conquered by Maharaja Ranjit Singh of the Sikh Empire in 1819, leading to the death of numerous Muslims in Kashmir, including some of Arbaaz's kin. This led Arbaaz to grow up with a resentment towards Singh, considering him a cold-blooded killer.
- Hamid: "Arbaaz. Take care. The diamond... The transcription reads: 'He who owns this diamond will own the world, but will also know all its misfortunes. Only God, or a woman, can wear it with impunity."
- Arbaaz: "I don't believe in curses."
- ―Hamid and Arbaaz, before the latter's departure, 1839.[src]
In 1839, Hamid tasked Arbaaz with the recovery of a map detailing First Civilization artifacts, most notably the Koh-i-Noor diamond, a powerful Piece of Eden. Upon his safe return to the Assassin headquarters in Amritsar, Hamid informed Arbaaz of the legend surrounding the Koh-i-Noor, and that the British Templars were attempting to obtain the artifact. The Koh-i-Noor had been in the possession of Ranjit Singh since 1830, who kept it safe from the hands of his enemies, but was nearing the end of his life.
As Singh's heirs were not as interested in the diamond as their father, the British Templars aimed to take Singh's life. Hamid tasked Arbaaz with ensuring the Maharaja's protection, an objective he reluctantly agreed to, but only for the sake of the Brotherhood. Before leaving, Arbaaz bought Hamid's slave Raza Soora from him, noticing the harsh treatment the boy was receiving from Hamid.
Arbaaz instead intended to find the Koh-i-Noor himself ahead of the Templars. Taking up the disguise of an emissary from Kashmir and his servant, Arbaaz and Raza entered Ranjit Singh's summer palace, where the Maharaja held a feast. Believing the Koh-i-Noor to be kept in a hidden chamber underneath the palace, Arbaaz told Raza to look out for Singh's treasure keeper, Bustee Ram.
After being allowed to join the feast, Arbaaz was greeted by William Hay Macnaghten, assistant to the British Governor-General of India – Lord Auckland – and General Francis Cotton. Arbaaz recognized the Templar insignia on Cotton's chest, though Cotton also identified Arbaaz as an Assassin by his movements. After Macnaghten left, Arbaaz assured Cotton that they were not enemies, telling the Templar that he had his own reasons for Singh's death, and that "it wouldn't be the first time [he had] to clean up after [their] kind".
Soon after, Arbaaz's attention was caught by Princess Pyara Kaur, Ranjit Singh's grand-daughter. Upon noticing Singh handing Bustee a diamond, Arbaaz told Raza to follow him and that he would find him later, deciding instead to follow Pyara. Arbaaz then tracked her to the palace courtyard, handing her a oleander blossom that he had swiped from the palace's dining room. As a result of the conversation that stemmed from the gesture, the two later shared a moment of intimacy.
Afterwards, Arbaaz proceeded to find Raza and follow him to the hidden chambers underneath the palace, which was activated by a water-based mechanism. Exploring the caverns filled with statues of Hindu gods, Arbaaz found a chest containing the diamond, but quickly dismissed it as a worthless replica. Upon further exploration, they stumbled upon illusionary walls and other statues left by the First Civilization.
There, Raza found the real Koh-i-Noor in a pool of water contained within the hands of the statue Durga; unbeknownst to them, their progress had been tracked by Cotton. Upon their return to ground level, Arbaaz was arrested by Singh's men, who had been alerted by Cotton and Macnaghten. It was at this point that Arbaaz hid the real Koh-i-Noor under Raza's turban, enabling the latter to escape with the artifact, while Singh's men took the replica.
Singh's men placed Arbaaz in a cell, though some time later, Pyara Kaur and Raza Soora came to see him. It was during this meeting that Pyara released him from his imprisonment, after Arbaaz told her his task of ensuring her grandfather's safety.
To Arbaaz's surprise and disapproval, Raza had given the Koh-i-Noor to Pyara, thwarting his plan to escape with the artifact and leave the Maharaja to fend for himself. After Pyara informed Arbaaz that Singh was drinking tea with the British, Arbaaz and Raza hurried to the imperial palace, the former begrudgingly so.
Scaling the structure, Arbaaz eliminated the patrolling guards as Raza stayed close behind, at one point turning back to prevent Raza from falling to his death. The two then separated, with Arbaaz infiltrating the palace's interior by leaping into the main hall from above, knocking Macnaghten over upon his landing and attacking Cotton with a chakram.
Following this, Arbaaz roughly slapped the tea cup from of Singh's hands, perceiving that it was poisoned; despite this, Cotton informed Arbaaz that he was too late to prevent the Maharaja's demise. Responding in his weakened state, Singh took out his blade to attack Cotton, calling the Templar a "coward" and "deceiver", while further going on to state that India would not fall to his Order. Cotton instead called the guards, yelling that the Maharaja was under attack by an assassin – Arbaaz.
Arbaaz fled the hall, followed by Cotton and Singh's men as he made his way to the courtyard. There, while Arbaaz was fighting imperial guards, Cotton tried to kill Pyara and take the Koh-i-Noor, but was halted by Raza, who dug his fingernails into the Templar's forehead. As Cotton turned on Raza, Pyara activated the Koh-i-Noor, taking up the appearance of a member of the First Civilization, sending a message for humanity to Jot Soora, who was experiencing Arbaaz's genetic memories through the Brahman V.R. in 2013.
Cotton instead attacked the entity, firing at it with his gun, and accidentally destroyed the Koh-i-Noor. Seeing the entity become enraged, Arbaaz took Raza and dove into the water, before the entity released a burst of energy across the area, killing Cotton and all the remaining guards.
Arbaaz later had a child with Pyara Kaur and became an ancestor to actress Monima Das, the fiancée of Jot Soora.
- Arbaaz in Urdu means "eagle", while Mir is a Punjabi clan or tribe between present day India and Pakistan. Mir is also a loanword from the Arabic emir, amir, and thus has the meaning of "leader, commander, prince" in aforementioned places.
- Arbaaz was the only known Assassin to wield a Hidden Blade which could divide itself into three blades.
- Arbaaz was one of the individuals who possessed the ability to use Eagle Vision.