Deimos gets to take centre stage in the Grell and Colletta story in Warlord 20 (April 1979).
And geez, what a spectacular splash page the issue gets! Travis Morgan, Tara, Machiste and Mariah Romanova finally approach Deimos' castle, which is located near the Arctic opening to Skartaris. This region is, indeed, the "end of the world," and there is a terminator line where the eternal sun never illuminates.
Deimos is thrilled that Travis Morgan has arrived, and puts his evil plan into action. He cuts Joshue Morgan very slightly. Ashiya is worried for the child, but Deimos does the boy no harm. Instead, he takes the cells he has removed and quickly clones a duplicate child, then has Ashiya hide the real boy.
When the group reach the castle, Deimos uses his control over the gates and bridges to separate Morgan from the rest of the gang, and bring him to him.
We see that Deimos now is immune to all injury, after Morgan stabs him right through the chest. Deimos is in a chatty mood, and explains how Morgan helped resurrect him by acquiring the mask for Ashiya, and also how his body is always on the verge of degenerating, and the potion he needs to stay healthy.
Then he gets around to showing Morgan his son, not explaining that it is a clone. He makes the boy age to manhood, an announces that Morgan will have to fight his own child, to the death.
Yup, Deimos be evil.