White Zetsu were originally twisted beings Kaguya had created from humans whose chakra had been drained dry by the God Tree.
For humans in the shinobi world, chakra and life were intimately linked. The instant a person exhausted their chakra, they died, let alone if it was forcibly drained from them.
Yet White Zetsu were "life" born from these already dead human bodies.
In a sense, White Zetsu were also life born of the God Tree, entities on the same level as its fruit.
Except the fruit was the essence, and they were the dregs.
They possessed an innate resistance to chakra, which was one reason Kaguya considered them a trump card against the Ōtsutsuki.
As an Ōtsutsuki, Kaguya had always worried that her clansmen might come looking for her. After all, she had violated the Ōtsutsuki Clan's rules.
Later, after Kaguya was sealed away, Black Zetsu took control of the White Zetsu and continually developed their capabilities.
For instance, they could take on the appearance of any human, becoming virtually indistinguishable from the original. Even the most sophisticated sensory ninjutsu could not tell the two apart.
They also had almost no limit to their lifespan. Though living beings, they could endure for ages; White Zetsu born in Kaguya's era were still alive and kicking today.
All these abnormalities demonstrated just how different they were.
Unfortunately, Black Zetsu, who had been using them all along, was wholly devoted to rescuing his mother and treated them as nothing more than tools.
Later, Black Zetsu revealed their existence to the elderly Madara Uchiha. Madara, wholly absorbed in his "Eye of the Moon" plan, likewise viewed them as tools and left them to Obito.
Obito was even more obsessive, wanting only to finish "creating a world with Rin in it"...
Thus, two generations