Batman helped found the Justice League of America (and worked with many, many heroes over the years in the Brave and the Bold), but there came a day when the JLA just wouldn't help, and Batman needed his own team....
his origins before....and even his team-ups with Green Arrow, with Superman, and even mystical heroes, and Batman even worked with Metamorpho and Black Lightning in issues of Brave and the Bold (Metamorpho in Brave and the Bold #68, #101, #123 and #154, and Black Lightning in Brave and the Bold #163), but as time progressed, Batman just found it easier to work with himself (which was an odd focus of the first story in Brave and the Bold #200, July, 1983).
That was part of the problem. When the financial adviser to Wayne Enterprises, Lucius Fox, was taken hostage in Markovia, the JLA wouldn't help Batman free him. So, Batman felt the need to leave the group, and headed there to free his friend in Batman and the Outsiders #1 (August, 1983).
early appearances of Metamorpho in Brave and the Bold, and then Rex went on to his own series, that lasted 17 issues from July-August, 1965 to March-April, 1968 (where Rex faced menaces like Kurt Vornak, Edifice K. Bulwark, Achille Le Heele, Doc Dread, El Matanzas, Stingaree, Franz Zorb, the Thunderer, Jezeba and Mr. Shadow, and working with Urania Blackwell the Element Girl), with Rex making a notable appearance in Justice League of America #42 (February, 1966, by Gardner Fox and Mike Sekowsky), wherein "Metamorpho Says - No!" to the JLA! Metamorpho wasn't interested in being a hero, he was looking for a cure to his condition (even though it helped him be a hero), and ended up in Markovia at a time of unrest looking for Dr. Helga Jace...
the Thorn) starting with Black Lightning #1 (April, 1977, by Tony Isabella and Trevor Von Eeden).
Merlyn the Dark Archer, Talia Al Ghul, the Cyclotronic Man (a renamed, old foe of Batman's), Synoide, the Annihilist, Flash foe the Trickster, but mostly Tobias Whale, the local leader of the 100. Black Lightning also worked with Green Arrow (proving they were both street level heroes, and inspiring Green Arrow to leave the JLA for a while), Superman and Batman, and even told the JLA no as well in Justice League of America #173-174 (December, 1979 and January, 1980, by Gerry Conway and Dick Dillin), before heading home, and losing his powers in Detective Comics #490-495 in 1980, and then being recruited by Batman to help free Lucius Fox in Markovia.
Black Lighting and Metamorpho were the two previous introduced heroes, but there were more in Markovia, and they were all introduced in the back-up story in Brave and the Bold #200 (July, 1983 by Mike W. Barr and Jim Aparo), though that story featured an already formed Outsiders team operating in Gotham (with a story taking place between Batman and the Outsiders #3 and #4).
As Halo, she could generate aura of different colors, and while she could fly with each, each color also had another power, like red was heat blasts, orange was force blasts, yellow was bright light, green was a stasis beam, blue was a distortion effect, indigo was a tractor beam, and violet...was unknown to Gaby (but allowed the violent Violet Harper control). Halo was taken in by Katana, who saw her as a surrogate daughter).