Hashirama Senju

The first Hokage, Hashirama Senju, lived many years before the start of the Naruto series. He, along with his brother and Madara Uchiha, founded the village of Konohagakure and gave rise to the idea of a village governed by ninja. I personally believe him to be the most powerful ninja of the last 100 years (at least). He single-handedly defeated both Madara and the Nine Tailed Demon Fox at the same time, saving Konoha from destruction. Despite his power, he died at a fairly young age. He was married to Mito Uzumaki, and is therefore somehow related to Naruto Uzumaki. He was the grandfather of Nawaki and Tsunade, the Fifth Hokage, teacher to the third, brother to the second, and some sort of in-law to the fourth.
One of the things that made him unique, and that is demonstrated in the picture above, was his wood-style ninjutsu. It is a kekkei genkai combining water and earth chakra natures. Only one other person in history (Yamato) is known to have used wood style.