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Kirk Langstrom is a scientist that was turned in a bat-like creature after one of his experiments, being known as Man-Bat. He then became a formidable adversary to Batman.
Kirk Langstrom developed a serum that transformed him into a bat-creature. This has made him a formidable adversary to Batman.
Man-Bat reappeared to Bruce during one of his nightmares, while he was wandering near his family cemetery.