The Isu (or Those Who Came Before, the First Civilization, or the Precursors) are an ancient and highly-advanced species of humanoid beings who were active on Earth several millennia before the rise of even the most ancient human civilizations in the Assassin's Creed Universe. The Isu created powerful artifacts and weapons that augmented their already superhuman abilities, and created the human race itself.
The Isu ruled over Earth roughly 77,000 years ago, before they were largely wiped out, alongside their human creations, during a great war with them. Their legacy would live on for thousands of years through myth and legend via many human religions. Their artifacts were desired by both the Templar Order and the Assassin Brotherhood, who waged a war of their own for control of them.
The Isu possessed six senses, the sixth being referred to simply as 'knowledge'. The Isu were also a highly technologically advanced and powerful race that some to predict and attempt to influence possible futures. Some individuals stood a full 20 inches taller than human. Although the Isu had a naturally longer lifespan, they were not immortal.