Olive Man's head is a small ball I found in the backyard which I painted olive green. I mounted it on the body of an alien figure. I accomplished this via one of my favorite figure mod techniques. I use an awl to poke holes in the parts I want to join and then use a portion of paper clip as a support. Then add a dab of super glue to hold it together.
Then I used epoxy to secure Olive Man to the battery pack.