Green’s Dictionary of Slang

doer n.1

[do v.1 (1a)]

a womanizer.

[UK]Shakespeare Measure for Measure IV iii: All great doers in our trade.
[UK]Davies of Hereford Scourge of Folly 93: Why then he lou’d a man and woman too; But lou’d them passing well that well could Doo. Go too then Lotus, sith you are a dooer.