Dr. Filius is a scientist operating out of a Submarine located in the center of a planetoid in the Netherworld. He was not native to that universe, but was somehow trapped there. He later joined Chris DeLuca aboard the Featherpool Ship. Before meeting Chris, he survived in the Netherverse by living in a submarine of his own invention in the liquid center of the First Planetoid. He also conducted physics experiments on the world around him.
When he met Chris, he was impressed to meet him, having heard tales of his many adventures. Also, he was happy that Chris' ship was able to help him conduct experiments on the Eye, which hadn't previously appeared long enough to be tested. (Chris Series: "Perceptual Boundaries")