public enemy number one

noun2

1. •
   (figurative) A person, organization, or other object considered to be particularly menacing, harmful, or loathsome.

   • The fact is that Reaganomics slowed down the breakneck economy and succeeded in defeating public enemy number one, runaway inflation. — 1983
2. •
   (US, old-fashioned) A person who ranks highest on the federal government's prioritized list of wanted criminal fugitives.

   • John Dillinger, America's Public Enemy No. 1 and the most notorious criminal of recent times, was shot and killed at 10:40 o'clock tonight by Federal agents. — 1934