Not sure I can fully answer this, especially as regards the pop culture aspect, but I will throw my two cents in.

The beatniks are an outgrowth of the Beat literary movement. Early outstanding figures in this movement are Allen Ginsberg, Jack Kerouac, William Burroughs, and Neil Cassady. It is worth noting that Cassady himself did little to no writing; however, he was enormously influential upon the other beats, especially Kerouac and Ginsberg. Cassady figures extremely prominently in Kerouac's epoch making novel On the Road as the inspiration behind the character Dean. Similarly, Cassady is mentioned by Ginsberg in Howl as "the secret hero of these poems":

who went out whoring through Colorado in myriad stolen night-cars, N.C., secret hero of these poems, cocksman and Adonis of Denver--joy to the memory of his innumerable lays of girls in empty lots & diner backyards, moviehouses’ rickety rows, on mountaintops in caves or with gaunt waitresses in familiar roadside lonely petticoat upliftings & especially secret gas-station solipsisms of johns, & hometown alleys too

Howl created something of a public stir, as it's unapologetically sexually explicit content (not to mention its biting honesty) lead to a prominent obscenity trial. Here is an NPR article regarding the importance of Howl and the resulting legal dustup.

The truly seminal work of the Beats in terms of public awareness and consciousness, however, has to be Kerouac's On the Road, which is often still assigned in high school and college literature courses.

I don't want to ramble too much about the literary history here, since that doesn't seem to be entirely congruent with your original question. If, however, you are interested in a good single-volume selection of Beat literature, The Portable Beat Reader would be a good place to start.

As I understand it, the beatnik persona developed in the aftermath of the Beat movement and was comprised primarily of those who identified with the movement's free expression and countercultural themes.