I suppose the Romans started it first, creating a law and then naming it for the man who framed it; thus the Lex Canuleia, a law of the Roman Republic named for the tribune Gaius Canuleius etc.
Most "laws" bearing someone's name nowadays are not rules prescribing action, rather they are observations about how nature works or about how people in fact behave. Some are formulated as a joke but prove their worth over time. Thus Parkinson's Law (Work expands so as to fill the time available for its completion); if you read the book of the same name, it's obviously meant to be a satire. Then look at the way that many large organisations actually behave, and its accuracy is clearly seen.
There are some other more recent "laws" of this kind that I think deserve to be better known. So If anyone feels like putting them on a blog that someone other than my devoted fiancée and a few other patient friends read, feel free to copy-and-paste!
Zuhlsdorf's Law: That pontifical legislation about Latin will always contain a[t least one] mistranslation into English.
Neuhaus's Law: Where orthodoxy is optional, orthodoxy will sooner or later be proscribed.
Hannan's Law: that no [political] party is Euro-sceptic in office. It's also known as Hannan’s First Law of Politics and is named for Daniel Hannan a Conservative English MEP. (Although he cites it and refers to it on his Daily Torygraph blog, he never actually states explicitly his own formulation of the law.)
Finally O'Hanlon's Law: No Catholic can ever tolerate another Catholic being further to the "right" than he is himself.
It's attributed to Fr David O'Hanlon, sometime curate of Kentstown in the diocese of Meath. It's certainly borne out in my experience; e.g. Indulterers (as one wag nicknamed us) generally dislike the SSPX who in turn fight with the Feeneyites. On the other hand, Opus Dei or the LCs are generally uncomfortable with Trads but are in turn often disliked or resented by diocesan clergy. And so on and so forth ...