der/da - last part of 'rider' or 'rida'(since final 'R's are difficult to pronounce in Japanese)
Based off of the manga made by Shoutaro Ishinomori in the mid to late 1960's, Kikaida/Kikaider is a series that uses the 'pinnochio' concept and asks the question "What defines 'human'?"
It started out as a four volume manga and then was made into a live action show around 1972-74. It also led to the creation of the Kikaider 01 manga which is supposed to focus on the story of Jiro's older 'brother'-Ichiro, or Kikaider 01. Kikaider plays a role in this shorter 3 manga volume series as well.
"The difference between your robots and Kikaider is that he has a conscience circuit..."-paraphrased from Saburo in the episode "Destroyer" from the Kikaider animation series.