The First Hokage's Greatest Weakness In Naruto
Throughout "Naruto," the First Hokage is a character who is often referenced but not often seen. When the story first kicks off, Konoha has lost its fourth Hokage 12 years prior and is currently being run by its third, who comes out of retirement to pick up where number four leaves off. For many episodes, the Hokage that are in power before numbers three and four are wrapped in mystery. Viewers don't even know their names, what important things they do, or what they look like as anything other than a Rushmore-esque rock sculpture.
However, what we initially do know about the First Hokage (prior to his eventual resurrection in "Naruto" and "Naruto: Shippuden") indicates that he is something very special. Characters refer to him as the "God of Shinobi" for his unparalleled skill and power. He's also almost single-handedly responsible for ending the Warring States period by making peace with the Uchiha clan and founding Konoha. However, Hashirama is not the perfect ninja people make him out to be. Even the father of the Leaf Village has his skeletons. Though, the First Hokage's greatest weakness might not be one you would expect.
Hashirama the gambler is a failed politician
On the battlefield, no man can truly match Hashirama Senju. He's just that good. As such, his real weaknesses lie deeper in his character. For instance, we know that (much like his granddaughter Tsunade), he loves to gamble. Friendly competitions are his bread and butter, and he's generally liable to wager his money on their outcomes. However, that's far less contemptible than Hashirama's true weakness: he is much too lenient of a politician to ensure the longevity of his most important policies.
Hashirama founds the Leaf Village through the union of the Senju and Uchiha clans. However, in the end, the Senju become the politically dominant family in Konoha, while the Uchiha are admonished for their past actions in the Warring States period. Hashirama always wishes to end systemic prejudices against the Uchiha and advises his successor (who is also his younger brother, Tobirama) to treat them with leniency. In retrospect, he should've done more. Inevitably, Tobirama continues to discriminate against the Uchiha, leading to their eventual coup and the subsequent Uchiha massacre. More so than his penchant for gambling, Hashirama's inability to secure political freedom for the Uchiha is arguably his greatest flaw.