While the most successful franchise that the now-legendary FromSoftware has spear-headed to date is undoubtedly Dark Souls and its various related games such as Bloodborne, there are a wealth of games by the company that really deserve more attention.
One of the franchises in this camp is Armored Core, which is also pretty big among Mech fans. Aside from this, there are series that are much more well-known in Japan that unfortunately haven't quite made it as big over here in the States, such as Tenchu and King's Field. As a result, today we'll be shining a bit more light on some series that don't get as much praise as they should, and specifically, backstories of some super cool bosses.
10 Owl
The first character to make an entrance here is going to have to be Great Shinobi Owl, the father of the titular character in Sekiro: Shadows Die Twice. While our first encounter with him is in a memory taking place in Hirata Estate, he does show up otherwise, and there's a bit of a twist involved. As far as his past goes, he taught Sekiro everything he knows, meaning that he's a masterful shinobi. We come to find out that he was a major player in the battle between the warring Ashina and Tamura clans but nevertheless was a wonderful father.
9 Seath
This name just might seem familiar to players of Dark Souls, since there's a particularly similar character mentioned in the lore of the game from the beginning, who was a major player in the war between men and dragons. Seath in Dark Souls was a traitor to the dragons and an ally to Gwyn, but his backstory in the King's Field series is slightly different. In King's Field, he's half of the Dragon God Vallad, who split himself. There is a seed of evil that remains, and it slowly takes over the realm.
8 Reinhardt The III
It's actually rather difficult to find much information on Reinhardt The III, let alone find a copy to play. That's because the game was only actually released in Japan, and anything other than that release would be one of the various fan translations.
That being said, there are a few things we know about him. That would be that he's incredibly interested in collecting ancient artifacts, likely the reason that he looks like a giant tree in his boss fight.
7 Mei-Oh
Mei-Oh is an infernal demon lord, and the final boss of Tenchu: Stealth Assassins. Tenchu, for those not familiar, is another one of the earlier franchises that FromSoftware created. It's a third-person action stealth game, in which you play as Ayame, although there are a few other important characters. Mei-Oh is the one pulling the strings behind all of the enemies that attack the player, and when defeated, is rather upset he was killed by a mere mortal.
6 Guyra
Another Dragon that's extremely reminiscent of one we might have seen before in Souls games, is Guyra. Guyra is the boss in King's Field 2, simply known as King's Field in the west. Guyra is a black dragon, the mirror to Seath. He was involved in the split of the one original god and was the first to fall to evil in their battle. Seath and Guyra fought for ages, to prove who was the strongest. After Guyra was slain, Seath descended into madness, unobstructed.
5 Divine Dragon
The Divine Dragon in Sekiro: Shadows Die Twice, is a rather mysterious creature. We don't know much about it, even with all of the lore that shows up in the game. Instead, we can postulate that perhaps, this dragon is the source of the rot.
Beyond the gates of the divine realm, there lives a dragon who is sickly and corrupted. The Divine Dragon is this dragon, still worshipped by monks on the outskirts of the entrance to the area.
4 The Controller
The Controller, something like a central nervous system for the world in which Armored Core takes place, isn't quite what it seems to be. In fact, one of the most commonly known enemies and antagonists in Armored Core is a hivemind of rogue AI, which is a byproduct of The Controller itself. The issue is that while The Controller is set up to make everything run smoothly, it degrades over time, leading to the breakdown of society.
3 Seed Of Evil
The Seed of Evil is perhaps best considered as being the third part of Vallad, the piece that was left after he split into Seath and Guyra.
This Seed, rather than being half-good and half-evil by its brothers, brings evil into the world after Vallad splits himself to seek further self-realization by separating himself. The seed grew further and further until it infected the entire world with its darkness.
2 Nine-Ball/Hustler One
In Armored Core: Master Of The Arena, we meet Nine-Ball, the pilot of an armored core that has never been defeated since the very inception of the arena. While this pilot doesn't frequently challenge people who approach to prove themselves, it's been shown time and time again that they aren't anyone to mess with. That being said, we find out it's piloted by a rogue AI, perfect in almost every way.
1 Demon Of Hatred
The Demon Of Hatred is a character that players who take on the burden that is completing Sekiro: Shadows Die Twice meet early on. The sculptor, sick with dragonrot and endlessly fashioning new tools and shinobi prosthetics for Sekiro, his fate is a strange one. Eventually, he's consumed by his baser impulses and becomes The Demon Of Hatred. We learn also learn that in his past, he was a prodigious Shinobi who was nearly turned into a Shura, a man who has lost touch with humanity and only seeks blood.