Roberts spent much of his early career in New York City as a freelance commercial artist and director. He also worked as a photographer, with work displayed at the 1964 World's Fair, and contributed cartoons to Playboy and The New Yorker. He soon became a popular designer for animation, creating character model sheets for Terrytoons and UPA projects. Roberts' style, reflecting his commercial illustration background, involved flat but appealing forms and a minimal color palette; most of his characters were white blobs with occasional splashes of color.
For Sesame Street, Roberts created Jasper and Julius, two characters who would engage in debates over body parts, as well as Christopher Clumsy. These characters were brought over to Roberts' Sesame Street strip, alongside Big Bird, Oscar the Grouch and Cookie Monster.
- see also: Poverty Pictures segments