Frank Stack is probably most well-known today for illustrating much of Harvey Pekar's American Splendor and Pekar and his wife Joyce Brabner's graphic novel Our Cancer Year. He has been a cartoonist in the underground scene for decades, ever since he befriended the much more well-known Gilbert Shleton (creator of The Fabulous Furry Freak Brothers amongst other things).
However, his Jesus comics are landmark comic strip series, as they are often considered the first underground comic strip. They were published in counter-culture publications in Austin and a humor magazine at UT Austin founded by Stack called The Texas Ranger.
Shelton later collected a selection of them into a xeroxed "publication" which did the 1960s equivalent of going viral.
Stack has went on to be a professor at the University of Missouri, but he's now retired from there. However, until the 2000s, he also kept illustrating and writing underground comix from the 60s until then.
I think it's pretty obvious why he didn't publish these initial comic strips in his own name, but if you don't get it, he didn't want to get attacked by some crazy Texas Christian.
It's not too hard when you're Jesus, lol