Where does the phrase “eager beaver” come from and What does it mean?

Though its reputation has been questioned in recent years, the beaver has been long noted for persistent industry.

This reputation gave us the simile, “to work like a beaver,” some two hundred years ago. And, of course, industrious persons have long been likened to the beaver, “So and so is a veritable beaver.”

We English-speaking peoples are gluttons for rimes, as, witness, such compounds as pell-mell, hodge-podge, helter-skelter, so, within the past few years, some bright spirit did the best he could and began referring to some individual who was particularly, and somewhat offensively, avid in his industry as an “eager beaver.”