Maxwell Aeon Nuitari

The Senju clan is descended from the younger of the two sons of the Sage of the Six Paths who was born with the "body" of the Sage, inheriting his father's strength of will and physical energy and believed that love was the key to bringing peace to the world. The Sage grew to favour the ideals of his younger son over those of his older son, who believed that power alone was the true key to finding peace. Therefore, on his deathbed it was the younger of the two brothers that the Sage chose to name as his successor. The elder brother, bitter and hateful at having being denied what he felt was rightfully his to inherit, attacked his younger sibling. The Uchiha clan would descend from the elder brother, resulting in the bitter centuries-long rivalry between the Senju and the Uchiha.[2]

The Senju clan during Hashirama's era.
The Senju clan gained their fame in the era before the founding of the hidden villages. Where other clans focused on mastering one particular skill, the Senju were masters in all skills, from ninjutsu, to taijutsu, to genjutsu. Because of this, they were feared as "the clan with a thousand skills" (「千の手を持つ一族」, "sen no te o motsu ichizoku"), which gave them their name Senju (千手, "a thousand skills", "a thousand hands").
The most famous member of the clan was their leader, Hashirama Senju. His unique Wood Release ninjutsu even gave the clan the nickname the Senju clan of the forest (森の千手一族, Mori no Senju Ichizoku). This Wood Release, and his ability to control the tailed beasts, made him the greatest shinobi of his time.

The Senju's place at the top of the shinobi world was undisputed, but there was one clan that was able to stand up to them: the Uchiha clan. Whenever one country hired the Senju, their enemies would hire the Uchiha, and vice versa. This led to a rivalry between the two clans and, more specifically, between the leaders of the clans, Hashirama and Madara Uchiha.


The Senju and Uchiha form an alliance.
However, in a world of constant bloodshed, Hashirama had a dream of peace, and a great love for his fellow men. Known as the "Will of Fire" (火の意志, "Hi no Ishi"), this belief made the Senju clan propose a truce to the Uchiha clan. Weary of fighting, and persuaded by Hashirama's great charisma and negotiation skill, the Uchiha accepted, ending their bloody rivalry. Only Madara was against this truce, believing the Senju would one day destroy the Uchiha clan. He was forced to accept, but his humiliation wouldn't end there.
Some time after the alliance between the Senju and the Uchiha was signed, the Land of Fire hired them to stabilise its borders, and the clans created a permanent settlement within the country. Thus, Konohagakure was founded, and, with it, the system of one Hidden Village per country. As the system spread throughout the world, the constant violence stopped, and Hashirama's dream began to become a reality. But it would soon start again after Hashirama was elected as the First Hokage; a move Madara felt was a humiliation and made him decide to leave the new village, eventually returning to attack it.


The Uzumaki and Senju.
Throughout the years, the Senju retained their supremacy over Konoha, and made the village into what it is today. After the First Hokage's death, his younger brother, Tobirama Senju, stepped up to become the Second Hokage. Although likely not a Senju by blood, Hiruzen Sarutobi, who would become the Third Hokage after the Second's death, was trained by both the First and Second. His successor, Minato Namikaze, was the student of Jiraiya, who was a student of the Third. Tsunade, the Fifth Hokage, was not only a student of the Third, but also the granddaughter of the First and the grandniece of the Second. All of them strongly held to the Will of Fire philosophy.
It is unknown if the Senju clan still exists as an organisation since there are no known persons with the Senju name alive, although the Fifth Hokage, Tsunade, might have the Senju surname. It is very possible that the Senju clan disbanded into smaller clans and families, especially since they never had specific traits or techniques like the Uchiha or Hyūga clans with which to easily identify them. Their legacy however, lives on strongly in the hearts of the people of Konoha.