Dr. Skylander is a Blue Sentient scientist from Storm Racers. He created Cymtrax (and possibly the whole Rark, but this is not confirmed).
Dr. Skylander was first briefly mentioned by Cymtrax in Robot Rampage, though not by name.
In Zone Runners, the Undersea Force found the remains of his labatory, and found his journal giving a warning about the Red Sentients coming.
In Dark Fields, Darsun managed to dechiper more of the journal, and revealed Dr. Skylander wrote the journal. However, she had not heard of him before (though this could be due to her poor memory at the time in Season 1).
In Evil Alliance (Part 1), he is mentioned in the beginning, and Cymtrax reveals Darsun's brother (Korax) was responsible for Dr. Skylander's death.
In Evil Alliance (Part 2), he is mentioned once again, and everything comes together, all revealing about Korax destroying him and what not.
In Plight of the Red Sentients (Part 1), while Darsun manages to regain all of her memory, she briefly mentions Dr. Skylander and reveals he was the one who made the Double-Element Crystal to freeze the Red Sentients. Cymtrax did not want to sell him out, but Korax forced him to.