Green’s Dictionary of Slang

ramrod n.

[fig. use SE ramrod, ‘a rod used for ramming down the charge of a muzzle-loading fire-arm’ (OED)]

1. [mid-18C+] the penis [rod n. (1)].

2. [early 19C+] (also rod) a manager or leader, usu. a tough person or harsh disciplinarian.

3. [mid-19C–1900s] a landlord.