Hal Jordan, the Silver Age Green Lantern, had been given his superpowers and attendant responsibilities by The Guardians of the Universe. As such, Green Lantern usually was unaware of the day to day problems suffered by the denizens of his home planet, since Earth was just a small portion of the sector of space Hal was given to protect.
In 1970, that all changed as his teammate in the JLA, Oliver Queen, the Silver Age Green Arrow took Jordan to task for not getting involved with the social crises facing the people of Earth.
As written by Denny O'Neill and drawn by Neal Adams, the Green Lantern comic book series re-named and re-invented itself as Green Lantern/Green Arrow beginning with issue number 76, in an attempt to rejuvenate the comic and its flagging sales numbers. The book was critically acclaimed as one of the first attempts by mainstream comics to present real life social issues. The Emerald Duo took on issues such as racism, overpopulation, and in a memorable story, drug abuse when it was discovered that Green Arrow's sidekick, Speedy (the modern-day hero known as Arsenal) was a junkie.
The series remained Green Lantern/Green Arrow until the book was cancelled in 1972 with issue number 89. The friendship between Jordan and Queen remained strong, and in fact many of the changes that each character experienced in this landmark comic book series continued to affect each hero's life well into the 90s.
As chronicled in Zero Hour Queen faced off against Jordan, who had gone power mad and taken on the sobriquet Parallax. In order to stop Jordan from re-creating a multiverse (a la the one that existed prior to Crisis on Infinite Earths), Queen was forced to kill Jordan, bringing a friendship that had spanned nearly three decades to a most tragic end.
Queen's character was killed off soon after Zero Hour, but as is the norm in comics, nothing stays the same forever. Jordan is now that instrument of a higher power known as The Spectre (replacing Jim Corrigan who had been The Spectre since the earliest days of comics and the Justice Society of America) and Queen has been resurrected by none other than Kevin Smith, so it's possible the two will be able to one day reunite, though in a decidedly different fashion than in the past.