The original Justice League of America had seven members.
They were Superman, Batman, Wonder Woman, the Flash, Green Lantern, Aquaman, and the Martian Manhunter. This lineup first appeared in The Brave and the Bold #28, published with a February–March 1960 cover date.
The team was DC Comics’ successor to the Justice Society of America, bringing major heroes from across the publisher’s fictional universe together. The League received its own ongoing title, Justice League of America, later in 1960. Additional heroes joined during that series, which is why longer lists of Justice League members can make the original lineup seem larger.
A common mix-up involves Green Arrow and the Atom. Both became important League members, but neither was part of the original seven in The Brave and the Bold #28. Green Arrow joined in Justice League of America #4, while the Atom joined later. The classic seven-member lineup also inspired later “Big Seven” versions of the team.