In Tite Kubo's Bleach, few villains are truly sympathetic, since many of them are either traitor Captains like Sosuke Aizen or terminal schemers like Gin Ichimaru, but there is an exception: the Vasto Lorde-class Hollow known as Coyote Starrk.
The Espadas are the ten strongest Arrancar under Aizen's command, and most of them are bloodthirsty thugs, with varying levels of devotion to their supposed savior. The Primera Espada, ranked #1, is none other than Coyote Starrk. But, despite his power, he has a much different perspective than the other nine Espadas.
Coyote Starkk & Lillynette Gingerbuck, Hueco Mundo's Wandering Duo
Some time ago, an immensely powerful Vasto Lorde roamed the desert sands of Hueco Mundo, not even bothering to visit the world of the living at all. This being's spiritual pressure was so strong it would crush and kill any Hollow that got close, making it impossible for anyone to come near, resulting in an exceptionally lonely existence.
It was too strong for its own good and so decided to split itself in half and form its own friend. The result was the duo of Coyote Starrk and Lilynette Gingerbuck, who could at least keep each other company. But still, Coyote's spiritual pressure was too strong for other Hollows or spiritual entities to survive, and the loneliness continued. That is, until Sosuke Aizen approached the duo and offered them a place among the newly-formed Espadas.
Coyote became a full-fledged Arrancar, as did Lilynette, and they were given the white and black outfits of the Espadas. Coyote was also given his own mini-palace inside the giant fortress of Las Noches, including room for his friend, and Coyote's immense spiritual pressure granted him the rank of Primera Espada. He had a Zanpakuto, like the other Arrancar, but his true Hollow form was inside Lilynette, who had come from his original body.
Coyote and Lilynette were kept on standby, awaiting Aizen's orders. They weren't terribly proactive or especially motivated, setting them apart from the likes of Grimmjow Jaegerjaques. But they did see the other Espadas as beloved friends and comrades, a rare sentiment among the Arrancar under Aizen's command. But friends were all Coyote ever wanted.
Coyote Starrk, Ace of the Fake Karakura Town Arc
Coyote Starrk and Lilynette appeared partway through the Hueco Mundo story arc, but it was really just an extended cameo. Coyote and Lilynette could sense the death of Aaroniero Arurruerie, the 9th Espada, and decided to not take any action. It wasn't their job to avenge him, after all. But Coyote did take action when Kenpachi defeated Nnoitora, using a sonido to appear on the scene, capturing Orihime and taking her all the way back to Sosuke Aizen.
This move was to keep Ichigo busy and out of the way while Aizen made his move on the fake Karakura Town. Then, with other elite Espadas like Tier Halibel and Barragan Luisenbarn (the former king of Hueco Mundo), Coyote invaded the world of the living.
There, Coyote and Lilynette met two of the most elite Soul Reapers, Captains Shunsui Kyoraku and Jushiro Ukitake. Coyote wanted to just mime combat to impress Aizen, but the Captains insisted on fighting for real. During the battle, Coyote demonstrated not only his incredible speed, power and swordsmanship, but also his razor-sharp instincts and observational skills, impressing the two Captains. Coyote then used Lilynette to perform his released form, Los Lobos, and battled his opponents' Shikai.
Partway through the battle, the eight Visoreds appeared on the scene, and some of them helped fight Coyote. Despite being so outnumbered, Coyote fought back with vigor, using his cero-blasting pistols and exploding spirit wolves to deal heavy damage to his enemies. But in the end, he succumbed, and Coyote fondly thought back to how the other Espadas had become his friends. He died without regrets, caring nothing for Sosuke Aizen's own ambitions. Coyote had gotten what he longed for at last, and he was able to pass in peace.