Upright the King of Swords is read as intellectual authority, ethical judgment and command exercised through reason rather than force; reversed, as coldness, manipulation, or a sharp mind used against people rather than in service of truth.
As a person card, he is conventionally read as a rational, principled figure, a lawyer, judge, analyst or anyone whose authority rests on clear thinking rather than on charisma or force, and readers often use him to represent professional or institutional judgment specifically, distinct from the more personal, embodied authority the suit's other court cards can carry. The suit of Swords generally is read as the deck's most morally ambiguous, capable of cruelty as easily as clarity, and the King is usually treated as the suit's best case, intellect that has learned restraint, rather than as evidence the suit's dangers have been eliminated.
Waite's own printed meaning stresses power, command and authority with comparatively little of the explicit ethics later readers emphasize; the reading of this king as specifically fair and just, rather than merely powerful, has become more prominent over the twentieth century, a pattern common across several court cards, where later practice adds a moral dimension the earliest printed source states only implicitly if at all.
Reversed, the same clarity becomes cruelty, a mind that has stopped checking its conclusions against compassion, which readers generally treat as this suit's most characteristic failure mode across every rank.