In its heyday, Hour 25 featured numerous interviews with famous authors of science fiction and fantasy, in addition to luminaries of the scientific community.
Hour 25 was originally hosted by Katherine Calkin and Mitchell Harding, who were quickly joined by Mike Hodel after the first few months.
The trio's appreciation for the genre and differing tastes brought a unique quality to the program, which was an eclectic mixture of science-fiction news, reviews, readings, filk music, occasional on-air listener phone calls, interviews, and playing of science-fiction radio shows such as X Minus One and The Hitchhiker's Guide to the Galaxy.
Mike Hodel would join the on-air cast within the first few months, and with a now-permanent trio of co-hosts in place, Hour 25 began to take on its most well-remembered form.
Hour 25 also adopted a fan-friendly method of operation in Southern California; the outer door of the station was deliberately propped open during the program, allowing fans to come and go as they pleased.
[1] Hour 25 was also one of the first US radio programs to introduce the American audience to The Hitchhiker's Guide to the Galaxy before NPR gained rights and aired it.
After co-host/engineer Mitchell Harding departed from Hour 25 in 1981 to take a position at KCRW-FM, Hodel co-hosted the show with science-fiction and television writer Mel Gilden, who was then just beginning his career.
At this same time, Harding's engineering duties were taken over by Joe Adams, who would occasionally co-host shows that featured discussions of various comics.
When Harlan Ellison decided to leave Hour 25, he contacted writer J. Michael Straczynski and asked him to take over the show as its weekly host.
The show continued to interview such guests as Ray Bradbury, Norman Corwin, John Carpenter, Dean Koontz, Walter Koenig, Neil Gaiman and scores of other writers, directors and actors.
Amongst the regular pool of hosts and co-hosts during this era were Straczynski, DiTillio, Arthur Byron Cover, Steven Barnes and Warren W. James.
In 1992, Straczynski, DiTillio and Cover all left Hour 25 due to creative differences with KPFK station management—particularly with regard to language used on the air, and management's request for advance notice of the program's content.
A special 25th anniversary show aired in January, 1997, and featured several co-hosts from years past, including Mitchell Harding, Katherine Calkin, Mel Gilden and J. Michael Straczynski.
With the time restrictions of fitting into a specific radio station timeslot lifted, Hour 25 episodes now lasted anywhere from 60 to 150 minutes, depending on the subject matter and material available for broadcast.
After the first few weeks as a podcast, calendar listings were no longer read aloud but were instead posted on the show's website — although even this practice petered out in early 2002.
Dedicated author interviews became rare: after 2006, Hour 25 produced between 1 and 6 new episodes each year, usually centered around reports from Loscon, or readings of Christmas and/or Hallowe'en-themed science fiction stories.
"Jupiter, the Bringer of Jollity" from Holst's The Planets was also used, as well as Mike Oldfield's Tubular Bells and other mixed material.