|Kekkei Genkai:||Mokuton (Unique to Hashirama Senju)|
The Senju clan (千手一族, Senju Ichizoku) was considered one of the strongest clan in the ninja world after they seperated from the Uzumaki Clan during the war-torn era before the founding of the hidden villages. Together with their rivals, the Uchiha clan, they were responsible for founding Konohagakure and making the village into what it is today.
The Senju clan is descended from the Uzumaki Clan - which in turn descended from the younger of the two sons of the Sage of the Six Paths. He was born with the "body" of the Sage, inheriting his father's strength of will and physical energy. The Sage's younger son 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 - and thus passed down most of his powers to him. 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.
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 Senjus' 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.
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 stabilize 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 anew 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.
Aside from Hashirama Senju's unique ability to control wood, the Senju were known to be extremely skilled in almost all ninja techniques except for Fūinjutsu.