Ishida Mitsunari was a famous samurai from the Sengoku Period, and a loyal supporter of Toyotomi Hideyoshi.
Born in Omi Province, he was a vassal of the Azai family, but left their service after their defeat at the hands of Oda Nobunaga. He was eventually taken under the wing of Hideyoshi and became one of his most trusted retainers, though apparently he wasn't very popular amongst the other feudal lords, who believed that he was just a pen-pusher who wanted to steal power for himself.
Mitsunari's role suddenly became vital to Japan's future following the demise of his liege. As a faithful servant of the Toyotomi clan, he swore to protect Hideyori (Hideyoshi's son) and thus became a bitter enemy of Tokugawa Ieyasu, the other major contender for the shogunate.
In 1600, Mistunari led the Western Army during the Battle of Sekigahara (though technically the leader was another feudal lord, Mouri Terumoto—who unfortunately was the better general between the two of them). Despite having more troops and initially gaining the upper hand, he was betrayed by some of his followers who sided with Ieyasu, and was defeated. Mitsunari managed to escape thanks to the Heroic Sacrifice of his vassal and bodyguard Shima Sakon, but was eventually captured by the Tokugawa forces and executed.
It was believed that some of the factors include how despite fighting for the Toyotomi dynasty, Mitsunari had a rather nasty streak that didn't endear him to other retainers, admonishing several people that fought alongside him in the Korean Campaign (which was already a disaster). This led him to do several drastic things to ensure the support of the people, some blackmail included. One that backfired spectacularly was the time he decided to gather support by taking their family members hostage. One of them happened to include the daughter of Akechi Mitsuhide, Hosokawa Gracia. Despite her being the daughter of the traitor of Oda Nobunaga, that was still considered a dick move for Mitsunari and took away a lot of his popularity amongst the people, and even worse for him, Gracia arranged her own murder (she's Christian, she could not commit Seppuku anymore since it went against her new faith). Hosokawa clan leader and Gracia's husband, Tadaoki, was outraged at this, he formerly had plans to join Mitsunari, but after this, he signed up for Tokugawa instead.
The other big factor was the battle of Fushimi Castle. Mitsunari's forces, en route to Sekigahara, was stalled by a veteran Tokugawa general, Torii Mototada, who initiated a mighty last stand battle. Mitsunari was delayed for about 10 days, but he was victorious anyway. However, by the time he arrived to Sekigahara, Tokugawa has already amassed a majority of their forces, which led to the eventual betrayal despite the early upper hand. Had Mototada not delayed Mitsunari in those days, he might have held the upper hand or be victorious despite the betrayal (since the Tokugawa would be severely undermanned).
Fiction hasn't been kind to Mitsunari, as he's often depicted as a villain and a Smug Snake, usually opposed to a more or less heroic Ieyasu, though recent depictions have improved his image, and moreso during the decline of the Tokugawa shogunate, where he enjoyed a lot of positive portrayals alongside Sanada Yukimura and being the 'brain' of the Tokugawa opposition for Yukimura's 'brawn' (although due to his jerkish attitude in history, he's more likely to take the pragmatism route compared to Yukimura's honor-bound route). To contrast with Ieyasu's usual old man portrayal, Mitsunari fares better to the fairer folks, he's often portrayed as a Bishōnen when they get him to be the heroic person. One of the items to distinguish Mitsunari from others is his helmet, which tends to be full of furs that looked like hairs in addition of the other normal apparels. We can only chalk down to 'personal taste' on why he would wear such thing, but it seemed to reinforce his portrayals as pretty boys by modern writers.
Portrayals in fiction:
- In Samurai Warriors, Mistunari became a playable character from the second game onward. He's depicted as cold, sarcastic, yet doing what he thinks is right. He wields a giant folding fan and has a Kitsune motif, opposing Ieyasu's Tanuki motif. His consistent Japanese voice in this series is Eiji Takemoto, shared with Shibata Katsuie.
- In Sengoku Basara, Mitsunari is a blood-thirsty, white-haired youth who's utterly obsessed with avenging his liege Hideyoshi. He's also a skilled Iaijutsu Practitioner with Super Speed who, although single-minded when it comes to killing Ieyasu, turns out to be a very complex and tragic character. The more notably famous Tomokazu Seki is cast as him here.
- In Kessen, Mitsunari appears as the leader of the Western Army.
- Akanesasu Sekai de Kimi to Utau portrays him as a short-tempered Determinator with a bad mouth who tends to make lots of enemies. He is voiced by Tomokazu Sugita.
- Brave10, where he fulfills of usual role of wanting to ally with Yukimura against Ieyasu.
- In Shogun, Ishido is based on Mitsunari, and the main villain. Not that Toranaga is any better...
- In Onimusha: Dawn of Dreams, Ishida Mitsunari appears as one of the main villains, having sold his soul and body to the Genma lord Claudius. He's also voiced by Norio Wakamoto.
- In Age of Empires III: The Asian Dynasties, Ishida Mitsunari is the main villain of the Japanese campaign.
- A younger version of Mitsunari, know as Sakichi, is the protagonist of Rengoku ni Warau, a prequel manga to Laughing Under the Clouds, where he's on a mission from Toyotomi Hideyoshi to find the Orochi.
- In Yo-Kai Watch, Whisper is revealed to have been the one to pass on stratagems to Mitsunari very long ago. Why hasn't it come up before episode 47? Because to Whisper, it's his biggest failure. This depiction is one of the most favorables to the general's character, and counts as a Shout-Out to Sengoku Basara, since both Whisper and Mitsunari are voiced by the same voice actor.
- Mitsunari is an antagonist in Nioh, alongside Shima Sakon and Otani Yoshitsugu as his most frequent aides, as the main protagonist William is siding with Tokugawa. Like most portrayals, he's driven to protect Hideyoshi's legacy that he found beautiful, but made the mistake of trusting Edward Kelley, who eventually backstabs him and left him Brainwashed and Crazy for William to defeat. Afterwards, he accepts capture and then sternly lets himself gets executed like in history.
- Ikemen Sengoku gives perhaps the most sympathetic portrayal yet of Mitsunari, depicting him as an incredibly sweet and kind-hearted bookworm who worships the ground Ieyasu walks on in spite of the latter's brusque treatment of him. It's nigh-impossible to imagine this Mitsunari ever turning against Ieyasu — then again, Ikemen Sengoku's premise of its time-traveling main character and Sasuke causing massive changes to the historical timeline means that it has a lot more wiggle room than most other media in its portrayals of its historical figures.