Maven: (n. מבין, from Yiddish via Hebrew, a person who understands). A self-proclaimed expert on any topic or issue; or, an actual expert on any topic or issue. Differentiating between a self-proclaimed maven and an actual maven requires the ability to determine whether the hubris of the former leads to any genuine knowledge or if the person is just a blowhard with a giant ego trying to show off, in which case the word can be used ironically. 

It is not clear when maven entered the English language, but its use became popularized in the 1960s when the spokesman for the Vita Herring Company was dubbed, “The Herring Maven,” a self-proclaimed moniker indicating that his knowledge of herring was superior to anyone else.