Here is the 1971 cover...
I cannot do it any better than he can, so I will let artist Bernie Wrightson explain (courtesy of this excellent interview:
I recall Len offered me the 'Swamp Thing' short story to draw that night. The deadline was really tight and I remember doing most of the work on a weekend. I had help from Kaluta, Jeff, Weiss and Louise. I remember that to save time we photographed the whole thing. The bad guy is Kaluta who could make himself look really oily. I parted his hair in the middle and he had this great moustache. Of course, I was the hero because the girl was Louise Jones, Jeff's wife, who I had a crush on and I got to put my arm around her.