Grell brings back Stryker, the CIA operative, in Warlord 13 (June/July 1978).
Travis Morgaan, Machiste and Mariah Romanova are still heading for Shamballah. It's taking them a long time to get there, and even Morgan is getting sick of this endless trek, so they go right through a swamp, instead of around it. They fight off a giant snake, which seems to die too easily.
That's because they had help. Stryker shot the snake. He has spent over a year on the track of Morgan and Mariah, ever since they got away from him at Machu Picchu. We learn that Morgan caused a cave in to conceal the entrance to the subway system that they rode into Skartaris, but Stryker managed to find it anyway. Stryker doesn't just want to kill Morgan, but to torment him. He binds Machiste and Mariah, and sends Morgan out to find the detonator for the C4 that his friends are bound to.
Of course there are some typical Skartarian hassles along the way as well. Stryker has left Morgan's gun on the track, but attached to another detonator, trying to trick him to kill his own friends.
Morgan evades both kids of traps, gets his gun and the detonator, and then shoots Stryker through his fake eye. Too bad, he would have made an interesting recurring villain.