Which spacecraft discovered Jupiter's ring system?

Voyager 1 discovered Jupiter’s ring system.

The spacecraft made the discovery in 1979 during its close encounter with Jupiter. The rings were unexpectedly faint and composed mainly of dark dust, so they were not easily visible from Earth. Voyager 1’s cameras detected the narrow main ring, revealing that Jupiter—like Saturn and Uranus—possesses a ring system.

Voyager 2 followed later in 1979 and obtained more extensive images, helping scientists refine the rings’ structure. Galileo then studied them in greater detail during its Jupiter mission from 1995 to 2003. The system includes a halo ring, a main ring, and two broad gossamer rings associated with the moons Amalthea and Thebe.

A common mix-up is Pioneer 11: its 1975 observations provided evidence related to Jupiter’s radiation environment and helped motivate later investigations, but Voyager 1 is credited with the visual discovery of the rings.