The Cartoon Network logo opens up to show Otto, Tuddrussel, and Larry inside; they activate their time machine transporter and disappear.
In the first season, the opening theme showed clips from the first season episodes on a black background with historical dates floating around. In the second season, the opening theme shows Larry, Tuddrussel, and Otto in paintings and sketchings of historical events and the three running while their attire changes to fit certain time periods.