Shepherd
Shepherd is a Marine inspector sent from headquarters to evaluate G-8, arriving aboard the Stan Malay after it gets hammered by a storm. He's the closest thing the G-8 Arc has to a real antagonist—constantly at odds with both the Straw Hats and the base's own forces. The running joke of the arc is that Shepherd has absolutely terrible luck. He gets mistaken for a Straw Hat pirate, accidentally helps the crew escape multiple times, and generally makes things worse whenever he tries to take charge.
Physically, Shepherd's a grayish-skinned guy with a ponytail who rocks the standard Marine overcoat over purple clothes and glasses. Robin steals his whole outfit at one point to impersonate him, and while he eventually gets his clothes back, he never quite recovers those purple glasses.
His personality is basically what you'd expect from a high-ranking Marine with an ego problem. He's arrogant, constantly threatening subordinates with court martial or decommission if they don't fall in line, and he's got an axe to grind with G-8's commander, Vice Admiral Johnathan. Shepherd thinks the base is a joke and Johnathan's leadership is useless, so he's determined to write a scathing report to get the place shut down—regardless of what's actually happening. He refuses help from Johnathan out of sheer pride, which predictably backfires and ends up protecting the Straw Hats instead. There's a cowardly streak in him too, especially once Johnathan gives him a look that makes Shepherd reconsider his attitude. He's got a lot in common with Spandam—that same kind of arrogant, self-serving officer vibe.
Shepherd doesn't have any special powers, but he's obsessed with his Eagle Launcher, a massive experimental bazooka from headquarters. It's got firepower comparable to a small battleship and works like a bird of prey's talons—hence the name. Problem is, he's not actually good at using it. The weapon does more damage to his own side than the Straw Hats.
When he first shows up, Shepherd's furious about the storm and the lack of a proper welcome. He refuses to tell lower-ranking Marines who he is or what division he's from, insisting he's a special VIP from HQ and shouldn't have to explain himself. He demands to see Johnathan immediately, but the Vice Admiral is too busy eating lunch to meet him. Frustrated, Shepherd decides to head to the command center on his own, planning to use his report to get Johnathan removed. Instead, he walks right into Robin, who takes him down and assumes his identity.
Later, when discovered locked up, the crew decides Shepherd has amnesia and actually goes by "Condoriano"—Usopp's ridiculous cover story. After the base figures out Robin was in disguise, Shepherd gets released and learns the Straw Hats are coming back for their confiscated gold. Ignoring the Stan Malay's captain's request to let his troops recover, Shepherd sees an opportunity to humiliate Johnathan and G-8 once and for all.
He corners four Straw Hats in the vault with his men and decides to handle it personally without listening to warnings about underestimating them. He pulls out the Eagle Launcher, aims it at the crew—and fires it backwards. With a little nudge from Robin's powers, his own weapon backfires on his marines and launches him into the air. The Straw Hats escape easily.
Next, Shepherd stations forces on Pine Peak to intercept the Going Merry at the sea gate and sink it before they can get away. This also spectacularly fails. The Pine Peak accidentally shows the Straw Hats exactly where the current is, and the Merry's disguise collides with the ship as they slip through.
When Shepherd realizes they're actually getting away, he hands things over to Johnathan—threatening to pin the whole disaster on him if he fails. Johnathan just tells him to include himself in the report as an obstruction. Shepherd watches helplessly as the base's special low-tide trap snags the Going Merry, then sneaks off for one last shot with the Eagle Launcher. While trying to aim at Luffy as the ship gets launched into the air by an Impact Dial, Shepherd accidentally destroys the turret targeting an octopus instead. It's the final push the Straw Hats need to escape.
After the arc ends, Shepherd threatens to decommission Johnathan for letting the pirates get away—never mind that Johnathan is Admiral Akainu's protégé. He gets a punch to the face from Jessica, Johnathan's wife, for his trouble. As the Straw Hats sail away and Johnathan laughs with his wife about the whole mess, Shepherd just lies unconscious on the ground.
Content compiled by AnimeList.moe from publicly available sources.