- "May the Father of Understanding guide us."
- ―A Templar blessing.[src]
The Father of Understanding is a subject often mentioned in reverence by Templars, particularly during ritual ceremonies, blessings or as a form of greeting to one another.
Symbolism and meaning
It has not been truly established whether or not the Father of Understanding refers to a metaphor or a literal entity, such as an Isu or even a higher being who is worshipped as a God by the Templars. Despite these speculations, The Father of Understanding does allude to the principle of order that the Templars embrace.
What it symbolizes is more important to them than what it is, personifying the logic the Templars appeal to in their dream to shepherd and transform the world and humanity as a whole into an eternally peaceful utopia which blossoms and advances under their supervision and leadership.
Since the Templars tried to establish the Cult of the Supreme Being in France at one point, it is most likely that the Father of Understanding is their version of the Monotheistic Supreme Being. This can also be referenced by the fact that they referred to him when greeting and blessing one another.
Between (431 – 404 BCE), during the Peloponnesian War, one of the precursor organizations to the Templar Order, the Cult of Kosmos, revered a mysterious entity called Kosmos as their deity and manifestation of their beliefs. Whether this has any connection to the Father of Understanding has never been mentioned or even discussed. 
In 15th March 44 BCE, when the leader of the Order of the Ancients, Lucius Septimius engaged in battle with the Hidden One Aya, she questioned whether Julius Caesar was the new king of the Order of the Ancients, to which Septimius replied that Caesar was the Father of Understanding.
In the Third Crusade, the Templars would usually sign his name before theirs in letters they wrote. During the Renaissance, Templars would often ask him for guidance as a greeting, or when resolving a social gathering.
Before and during the American Revolutionary War, the phrase was used three times by Haytham Kenway; first, during the induction of Charles Lee to the Templar Order in 1755, second, when inducting Shay Cormac to the Templar Order in 1757, and third, when Haytham was required to enter the Smith and Company Brewery with his son, Connor.
During his investigation into the Templars' affiliation with the Cult of Baphomet, Arno Dorian required a password to gain entrance into the cultist's lair. He was informed by another Assassin that the password was "The Father of Understanding". During the French Revolution, the Templar Maximilien de Robespierre tried to establish the Cult of the Supreme Being as the State Religion of France, basing the cult's theology entirely on the doctrine of the Templar Order.