Hashirama Senju was a shinobi from the Warring States Period, an era defined by constant conflict between small nations and rival mercenary clans. As the eldest son of Butsuma Senju, he and his brothers were forced onto the battlefield from a very young age to fight the clan's perennial rivals, the Uchiha. It was during this violent time that he met a boy his own age, Madara Uchiha. Unaware of each other's family names, the two formed a deep friendship, bonding over their shared loss of brothers and a mutual dream of ending the endless cycle of child warfare. Upon discovering their true identities as heirs to sworn enemy clans, they were forced to become rivals, though Hashirama never stopped considering Madara a friend.

Hashirama's defining personality trait is a striking contradiction between his immense power and his easygoing, almost naive nature. He is often depicted as excitable, boisterous, and prone to sudden mood swings, such as falling into exaggerated fits of sulking when things do not go his way before quickly perking up again. He loves playful competitions and gambling, a habit he would pass down to his granddaughter, Tsunade. This jovial demeanor often leads others, including his more serious younger brother Tobirama, to openly question how such a man could be the legendary God of Shinobi. However, this lighthearted exterior masks an unshakable will and a deeply serious commitment to his ideals. When the safety of the village or the dream of peace is threatened, Hashirama becomes a formidable and decisive warrior, capable of immense focus and terrifying resolve.

His core motivation is the protection of children and the establishment of lasting peace. After witnessing the deaths of his own younger brothers, he was driven to create a world where children would not have to die in battle. This dream led him to work tirelessly for an unprecedented alliance between the Senju and Uchiha clans, believing it was the only way to end their generations-long blood feud. This alliance resulted in the founding of Konohagakure, the first hidden village, which operated on the principle of the Will of Fire. This philosophy, which Hashirama embodied, holds that all villagers are part of a single family, and the Kage's duty is to protect that family at any cost, even one's own life. Although he brought a fragile peace and ushered in the age of hidden villages, he was ultimately unable to achieve a lasting world peace during his lifetime, a goal he left for future generations.

Hashirama's role in the story is that of a foundational legend. Though he dies long before the main events of Naruto, his legacy is the entire shinobi world as it is known. As the First Hokage, he is revered as the God of Shinobi, the strongest ninja of his era, and a paragon of the shinobi way. His actions, including the decision to distribute the tailed beasts among the five great nations to maintain a balance of power, directly shape the political landscape of the series. He is later reincarnated during the Fourth Great Ninja War, allowing him to interact with modern shinobi, witness his dream's enduring legacy, and battle once more alongside and against his resurrected contemporaries.

His most pivotal relationship is with Madara Uchiha. Their bond of friendship, rivalry, and eventual tragic conflict is the central pillar of his life. Hashirama always saw the good in Madara and constantly sought a peaceful solution, even offering to kill himself to end their war. Their final battle at what would become the Valley of the End is legendary, where Hashirama was forced to kill his friend to protect the village he built. His other key relationships include his younger brother Tobirama Senju, the pragmatic Second Hokage who often acted as a foil to Hashirama's idealism and whom Hashirama instructed not to mistreat the Uchiha. He is also the grandfather of Tsunade, the future Fifth Hokage, and was married to Mito Uzumaki, who became the jinchuriki of the Nine-Tailed Fox after its capture.

In terms of development, Hashirama evolves from an idealistic child who dreams of peace into a powerful clan leader and, finally, the founder and leader of a nation. While his core ideals remain unwavering, his later years see him confronting the harsh realities of governance, such as when he reluctantly allows money to be exchanged for tailed beasts at a Kage Summit, acknowledging that his pure vision might not be perfectly attainable. Later generations are surprised to find that the legendary, stoic figure from history is actually a very emotional and kind person, revealing a gap between the myth and the man.

Hashirama's notable abilities are virtually unmatched, earning him the title God of Shinobi. His signature power is the kekkei genkai Wood Release, which combines earth and water-natured chakra to create life. This allows him to instantly grow forests, construct buildings, and create massive wooden structures for combat. His most devastating technique, the Sage Art Wood Release: True Several Thousand Hands, manifests a colossal, multi-armed statue that can dwarf even the full Nine-Tailed Fox. He could also enter Sage Mode, which covered his face with distinct markings and dramatically amplified his already immense strength and jutsu power. Furthermore, Hashirama possessed an extraordinary healing ability that allowed him to recover from wounds without forming hand signs, a power that his granddaughter Tsunade would later attempt to replicate with her Creation Rebirth technique. His chakra reserves were so vast that they were compared to the nearly limitless energy of a tailed beast.