The original Guardians of the Galaxy were created by Marvel Comics. They first appeared in Marvel Super-Heroes in 1969.
The writer who created the Guardians team, featuring Major Vance Astro and others, was Arnold Drake, who also created the Doom Patrol, Deadman and many others. In fact he wrote the entire Doom Patrol story. The series was drawn by the well known comic book artist Gene Colan, who created The Tomb of Dracula as well as many other titles for Marvel.
After their first appearance the Guardians grew more and more famous, often appearing in stories with other iconic Marvel creations like Captain America. In the 1990s the Guardians had their own comic book series, though by this time the writer and illustrator was Jim Valentino, who would later create ShadowHawk and other titles.
The Guardians series is still famous, though since its original conception both the characters and the people who create them have had a good many changes. The latest writer to get involved with them is Neil Gaiman.