Definition of public enemy number one in English:

public enemy number one

(also public enemy no. 1)

noun

US
  • The first person named on a list of wanted criminals; the person regarded as the one it is most important to apprehend; (in extended use) that which poses the greatest threat to the welfare or security of a community, nation, etc.

Origin

1930s; earliest use found in The Coshocton Tribune.