The Friends and Foes of Green Lantern:

Hal Jordan - Harold "Hal" Jordan is the real identity of Green Lantern.  Selected by a dying member of the Green Lantern Corps to succeed him, Hal went on to become the greatest Green Lantern of them all.  Hal works as a test pilot for Ferris Aircraft.

The Green Lantern Corps - Think of the GLC as a universe-wide police force/army made up from the best and brightest from various races throughout the cosmos.  Armed with rings that project incredibly powerful green beams of energy, the only limitation on what the ring can do is its wearer's own will power.  A previously-existing weakness to yellow-colored objects has been eliminated.

The Guardians of the Universe - Powerful and immortal beings who live on the planet Oa, which exists at the center of the Universe.  The Guardians created the Green Lantern Corps and have charged them with the task of protecting the universe from all that would destroy it.  The Guardians also keep watch over the Central Power Battery, a giant lantern-shaped object that feeds power to each individual Corps member's smaller power battery and associated power ring.

Carol Ferris - Hal Jordan's on-again/off-again girlfriend.  She runs Ferris Aircraft on behalf of her father, Carl Ferris.  Carol and Hal have come close to marrying several times over the decades, but have never sealed the deal.  Today, Carol only appears infrequently in Hal's life as it appears they have chosen to go their separate ways for good.

Thomas Kalmaku - Tom is an Inuit (aka "Eskimo") who is introduced early on in the Green Lantern series as a mechanic at Ferris Aircraft.  In Tom's early appearances in the 1960s, he was given the unfortunate nickname of "Pieface," a play on Eskimo Pie.  Needless to say, that nickname was left behind with the 60s.  Tom was Hal's confidant and knew of Hal's double life as Green Lantern, and he would keep a running diary of all Hal's adventures as Green Lantern.  As the 1960s wore on, Tom was eventually phased out of the Green Lantern series, and he only made sporadic appearances throughout the 1970s.  However, he returned to prominence for awhile in the late 1980s as it was revealed that Tom had super powers of his own.  Tom became one of the so-called "New Guardians," but eventually that aspect of the character was dropped and Tom returned to Ferris Aircraft eventually becoming a partner.

Guy Gardner - A 1968 revision to Hal Jordan's origin story introduced Guy Gardner who, as it turned out, was also selected as a possible candidate to receive the Green Lantern ring by the dying alien.  In this revision, they were both equally qualified, but Hal was chosen simply because he was closer to the alien who had only minutes left to live.  After this single appearance in 1968, Guy resurfaced for a bit in the late 1970s.  However, during the 1985 DC Comics line-wide crossover event known as "Crisis on Infinite Earths," Guy became a major player in DC Comics for the first time.  He received his own power ring, and his brash, plays-by-his-own-rules attitude quickly made him a fan favorite.

John Stewart - During the aforementioned "relevance era" that changed the tone of the Green Lantern series, a young, African-American architect was chosen to be a backup Green Lantern to Hal Jordan.  John made his first appearance in 1971 in Green Lantern vol. 2 #87, and, like Guy Gardner, only made a few appearances throughout the 1970s before being pushed to the forefront in the 1980s.  When Hal Jordan temporarily resigned his post as Green Lantern of space sector 2814 in the early 1980s, John Stewart, as his backup, was appointed to Hal's position for a brief period.  Like Guy Gardner, John Stewart has since acquired his own fanbase separate from Jordan's and was heavily featured in the recent animated series, Justice League and Justice League Unlimited.

Kyle Rayner - In the mid-1990s, the Green Lantern series was suffering from another period of lower sales.  It was therefore decided to remove Hal Jordan as Green Lantern and pass the ring along to a new character who would, it was hoped, catch on with the fans and reignite sales.  Kyle did just that, and from 1994-2004 was featured as the main Green Lantern in DC Comics publications.  When it was decided to bring back Hal Jordan in 2004, Kyle stepped down as Earth's Green Lantern, but still appears as an important part of the Green Lantern Corps organization.  In recognition of his efforts, Kyle was made a member of the Honor Guard of the Green Lantern Corps.  However, the Green Lantern magazine was handed back over the Hal, and Kyle is now a supporting cast member of the companion series, Green Lantern Corps.

Sinestro - Chief among Hal Jordan's enemies is the disgraced former Green Lantern, Sinestro.  Once one of the greatest of the Green Lantern Corps, Sinestro turned evil and was stripped of his power ring and banished from our universe to the planet Qward, which exists in the Antimatter Universe.  While in exile, Sinestro encountered the Weaponers, evil rulers of Qward who shared his hatred of the Guardians and the Green Lantern Corps.  Forming an alliance, the Weaponers fashioned a power ring and lantern-battery based on yellow light energy knowing that, at the time, yellow was the one thing that the Green Lanterns could not affect.  In more recent times, Sinestro's evil influence grew even greater, and he created a so-called "Sinestro Corps" with each member having a yellow power ring to serve as evil counterparts to the Green Lanterns.  Fans of Saturday morning television may remember Sinestro from his appearances as part of the Legion of Doom on the 1970s series, Challenge of the Superfriends.

Star Sapphire - The above-mentioned Carol Ferris becomes the villainous Star Sapphire after a race of alien warrior women, the Zamarons, arrive on Earth and select Carol to be their new queen.  Presented with a sapphire crystal that grants her with identical powers to Green Lantern, Carol falls under its evil influence before being freed by Jordan.  However, over the years, Carol would re-encounter the crystal and become Star Sapphire on numerous occasions.