Monday’s Monster is Man-Bat
Dr. Kirk Langstrom, fearful that he is beginning to go deaf, develops a serum that will give humans a bat’s sonar ability. Not wanting to go through the normal protocol and having the lack of patience that all comic book scientists are known for; tests it upon himself.
The serum works but has the side effect of transforming Langstrom into a man sized bat. It also robs him of his human intelligence and he goes on a rampage of murder and destruction in Gotham until the Batman can step in and stop him.
Later on, feeling he has perfected his serum, Langstrom convinces his wife Francine to take it as well creating the She-Bat. She also goes on a rampage causing the Batman to once again step in.
The Man-Bat had the opportunity to become a class A villain, but was reduced to a fairly minor role in the Batman mythos. He was, what the Batman symbolically tried to be. A creature of the night that struck fear. Only instead, he was relegated to a caricature of a fright night B movie creature.
And that is just too bad.