The question is a bit unclear, but most people asking “who was in the Jackson…” mean “Who was in The Jackson 5 / The Jacksons.” The classic Jackson 5 lineup was five of the Jackson brothers: Jackie, Tito, Jermaine, Marlon, and Michael Jackson. Later, when the group performed as The Jacksons, younger brother Randy Jackson also became a full member, while Jermaine left for a period and then rejoined for some projects.

Core group members

• Jackie Jackson – original member and vocalist in all main eras of the group.

• Tito Jackson – original member, guitarist and vocalist.

• Jermaine Jackson – original member, bassist and vocalist, later left when the group moved labels but returned for some later work.

• Marlon Jackson – joined early on and sang vocals with the group.

• Michael Jackson – youngest of the original five and the lead singer who later became a major solo star.

Later addition

• Randy Jackson – youngest brother who initially played percussion with the group and then became a full member when the group’s name changed to The Jacksons and Jermaine stayed with Motown.

If you meant a different “Jackson” (for example Andrew Jackson or another Jackson group), say which one and the answer can be tailored.