He is the boss of this criminal organization.
The police finally arrested the leader of the gang.
彼は反乱軍の首領として知られている。
He is known as the chief of the rebel army.
警察は暴力団の首領を逮捕した。
The police arrested the leader of the gang.
The underlings faithfully followed their boss.
頭（かしら）is a colloquial term for a boss used in traditional or informal groups like craftsmen or gangs, while 首領 is a more formal word for the top leader of an organization.
ボス is a casual loanword for 'boss' usable for any workplace superior, whereas 首領 sounds more serious and often refers to the head of a criminal or rebellious group.
リーダー is a neutral loanword for the leader of a team or project, while 首領 carries a heavier, often underworld-tinged nuance.
親分 is an informal term for a boss with a paternalistic, yakuza-style nuance, while 首領 is a more formal, neutral term for the top leader of a group.
頭目 and 首領 are close synonyms both meaning the chief of a gang or band, with 頭目 sounding slightly more old-fashioned or literary.
首領 refers to the head of a gang, faction, or organization and can sound sinister, whereas 盟主 is neutral and specific to alliances.
首領 often carries a connotation of leading a gang or criminal group, while 領袖 is used more for political or organizational leadership.
首領 is a formal, often legal or journalistic term for the head of a criminal or rebel group, while ドン is a more colloquial, slang-like way to call the same kind of powerful figure.
首領 often carries a negative or criminal connotation (e.g. the boss of a gang), while 総帥 is neutral or even respectful, used for legitimate military or business leaders.
部下 refers to a subordinate who takes orders, the opposite role in a hierarchy from the 首領 who gives them.
首謀者 refers specifically to the person who plans or masterminds a crime or plot, while 首領 refers to the ongoing head or boss of a group regardless of any single scheme.
counter for people
Standard kanji form; used in news and general writing.
Rarely used kanji form; learners should prefer 首領.
Composed of 首 (head, chief) and 領 (territory, control). The combination naturally yields the meaning of a person who leads or controls a group.