Born and raised in England, Callender began his career as a stage manager with London's Royal Court Theatre (working on productions by such esteemed living playwrights as David Hare and Sam Shepard) before joining Granada Television as a trainee. In 1983, he formed The Callender Company, Ltd. and reached an international audience as producer of the nine-hour, Emmy-winning "The Life and Adventures of Nicholas Nickleby." Based on the Royal Shakespeare Company production of David Edgar's stage adaptation of the Charles Dickens' novel, the miniseries was the initial independently produced project to air on the then new Channel Four in Great Britain and was distributed worldwide by PolyGram. Among the other productions made under the aegis of The Callender Company were the 1985 CBS TV-movie "Arch of Triumph" and "The Bretts" (aired in the USA on PBS' "Masterpiece Theatre" in 1987 and a 1989). In 1987, Callender ventured into features, serving as producer of Peter Greenaway's "The Belly of an Architect" which starred Brian Dennehy in the title role and was the official British entry at the Cannes Film Festival. Callender joined Home Box Office in 1987 as executive producer of "HBO Showcase," which produced innovative films that brought together a mix of exciting new and established talent. "HBO Showcase" has presented dramatic fare based on actual events (i.e., "Tailspin: Behind the Korean Airliner Tragedy" 1989; "Dead Ahead: The Exxon Valdez Disaster" 1992) as well as originals such as "Criminal Justice" (HBO, 1990) and the Forest Whitaker-directed thriller "Strapped" (HBO, 1993). Many of the productions earned nominations and accolades ranging from CableACEs to Golden Globes to Emmy Awards. After some seven years and more than 25 telefilms, in January 1996 Callender was asked to serve as head of the newly formed HBO NYC Productions, which was devoted to "giving a voice to filmmakers whose different views of the world might otherwise go unheard." In its first 18 months, the division oversaw three of the networks most acclaimed cable movies: the triptych "If These Walls Could Talk" (1996), which examined the social history of abortion in the USA from the 1950s to the 90s; the award-winning "Miss Evers' Boys," based on David Feldshuh's stage play about the Tuskegee syphilis studies of the 30s and 40s; and "In the Gloaming" (1997), an AIDS-themed drama that marked the directorial debut of Christopher Reeve. Other noteworthy projects included the omnibus "Subway Stories" (1997), "Always Outnumbered" and "When Trumpets Fade" (both 1998) and "A Lesson Before Dying" (1999). In April 1999, HBO chair and CEO Jeff Bewkes announced plans to consolidate all original programming under one executive, Chris Albrecht, which was more in line with how other networks operated. Callender was also promoted to president, HBO Original Movies. Reporting to Albrecht, he now holds responsibility for the networks complete slate of original telefilms.