John Agar was my first favorite sci-fi hero when I was a young'un watching his movies REVENGE OF THE CREATURE, TARANTULA and THE MOLE PEOPLE. I was fortunate both to interview and get to know John later in his life (we never personally met but talked often by phone and through his fan club journal). He told me that while life was too short to hold regrets, one mistake he probably made was not re-signing the contract with U-I after THE MOLE PEOPLE. He said he asked for a guarantee that he wouldn't be featured exclusively in sci-fi films and wanted the same opportunities given other contract players, like Rock Hudson, Tony Curtis and Jeff Chandler. But VP Jim Pratt told John he could not promise him that, so John said no hard feelings but left the studio. (Actually John did make one non-genre film at Universal-International: the Western STAR IN THE DUST). The irony is the first film he made away from U-I was DAUGHTER OF DR. JEKYLL, then came the "classics" ATTACK OF THE PUPPET PEOPLE, THE BRAIN FROM PLANET AROUS, etc. Pretty much downward from there.
It's interesting to speculate on other sci-fi films John might have starred in had he stayed at the studio: THE DEADLY MANTIS, THE LAND UNKNOWN, MONSTER ON THE CAMPUS - perhaps the preacher in CURSE OF THE UNDEAD. I can easily see him in each of these movies.
On a personal note, it was John Agar who inspired me to write my first Western novel. I honored him by writing a character based on him. Great guy!