SV40, or Simian Virus 40, is a polyomavirus that was first discovered in the early 1960s in monkeys. It is known for its ability to cause tumors in laboratory animals and has been studied for its potential role in cancer research. The virus gained attention because it was found as a contaminant in some early polio vaccines, leading to concerns about its effects on human health. While SV40 is not known to cause disease in humans, its study has contributed to our understanding of viral oncogenesis and the mechanisms of cancer development.