He's Hassan. She's Hassan. They're all Hassan.

Name: Assassin, Hassan-i-Sabbah
Origin: Fate/zero
Gender: Varies
Classification: Heroic Spirit, Servant
Age: Unknown
Powers and Abilities: Super speed, strength, cant split into up to 80 beings
Weaknesses: None
Destructive Capacity: Varies
Range: Varies
Speed: Varies
Durability: Varies
Strength: Varies
Stamina: Varies
Standard Equipment:
Intelligence: Varies
Notable Attacks/Techniques:

Zabaniya, Delusional Illusion: Delusional Illusion is the Noble Phantasm of the Assassin seen in the fourth Grail War. It is ranked as an anti-unit Noble Phantasm, but the target really is Assassin himself.
Assassin is a single individual, but he is able to split his soul into multiple personalities, divide his spiritual potential, and materialize the equivalent of multiple Servants. He can split into at most 80 people. There is a chance for him to lose his sense of self by doing so.
The stats are also divided, so this does not really equal a small army.

Notable OBD Victories:

Notable OBD Losses:

Other: Not to be confused with the character of the same name from Fate/Stay Night

Not a very helpful profile, is it?