Captain Harlock is a space pirate embodying the archetypical Romantic hero, defined by individualist philosophy and rebellion against oppressive regimes. He sails the cosmos independently, declaring he fights "for no one's sake... only for something deep in my heart," reflecting commitment to personal conviction. His attire prominently features the number 42, a Japanese cultural symbol associated with death, underscoring his fearlessness toward mortality. He descends from the ancient Germanic Harlock clan of pirate-knights based in Heiligenstadt.

Before becoming a pirate, Harlock served as a Solar Federation military captain. His first command was the starship Deathshadow, later weaponized against him by adversaries. His path changed irrevocably after the Illumidas alien empire conquered Earth. This occupation claimed the life of his wife, Maya, and resulted in his banishment from Earth alongside key allies Tochiro Ōyama and Emeraldas. These events forged his transformation into an outlaw, leading the crew of the starship Arcadia – designed and built by Tochiro – in resistance against the Illumidas.

In "Endless Orbit SSX," Harlock pilots the Arcadia seeking the mythical "Planet of Peace" (Arcadia), a haven for humanity free from conflict and Illumidas oppression. His crew comprises individuals scarred by the occupation: the orphaned Tadashi Monono (initially a bounty hunter targeting Harlock), Kei Yuki (whose father sacrificed himself for the Arcadia), the child Rebi, and the alien survivor La Mime. Harlock demonstrates mentorship, particularly towards younger crew members like Tadashi and Rebi, guiding them through challenges despite his typically reserved demeanor.

His foundational relationship with Tochiro Ōyama is marked by profound mutual trust and camaraderie rooted in their ancestors' history. Emeraldas, commanding her own ship, the Queen Emeraldas, functions as his formidable female counterpart and occasional ally, sharing ideals though maintaining greater solitude. Harlock's primary antagonist is the human traitor Mr. Zone, a former colleague whose vendetta stems from a prior professional dispute and who collaborates with the Illumidas. This conflict embodies the series' thematic contrast between Harlock's humanistic resilience and Zone's cold, technological ruthlessness.

Harlock consistently exhibits exceptional combat and piloting skills during engagements with Illumidas forces or Zone's schemes. Typically stoic and emotionally restrained, rare instances – such as confronting the AI-controlled Deathshadow replicating his own tactics – provoke visible frustration and anger, revealing deeper emotional currents. His leadership prioritizes crew autonomy and free will; he values comrades fighting alongside him by choice, not obligation. The Arcadia's Jolly Roger flag symbolizes this commitment to freedom.

His character extends into broader media. "Arcadia of My Youth" depicts his origins and acquisition of the Arcadia, featuring flashbacks involving his 20th-century ancestors. "Gun Frontier" presents an alternate Old West version featuring ancestor Franklin Harlock Jr. as a sidekick to Tochiro Ōyama. "Endless Odyssey" positions him in exile after the 1978 series, returning to combat the cosmic entity "Noo." "Harlock Saga" reimagines him confronting god-like beings within a narrative based on Wagner's "Ring Cycle." The 2013 CGI film "Space Pirate Captain Harlock" offers another standalone interpretation. Across these portrayals, his core identity as a defiant, freedom-seeking icon persists.