THE BEAST WITHIN (1982)
Starring Ronny Cox and Bibi Besch
Really cool early 1980s horror film, replete with some of the most gruesome transformation effects I have ever seen, courtesy of make-up effects maestro Tom Borman.
A woman is (graphically) raped by a monster and gives birth to a son who finds himself entering adulthood with mysterious homicidal impulses. Naturally the adult son (Paul Clemens) slowly transforming into something close to the rampaging, murderous beast his father was.
Well-scripted—with a plot involving the son's parents searching for some clue as to what created him and local townsfolk unwilling to reveal the truth—and full of gore, this is a must-see gore movie. They don't make 'em anymore like this, kids. Tom Holland, who wrote the screenplay, went on to become a major horror filmmaker, directing the excellent "Child's Play" and "Fright Night."
Highly, highly, highly recommended, this classic film wowed every teenage horror fan alive when it came out in the early '80s, and maintains a following today among those of who shun CGI.