Wordorigins.org

The original sense of dork is penis. It is probably an alteration of dick, dating to the early 1960s.

From Jere Peacock’s 1961 novel Valhalla, in a reference to 1953:

You satisfy many women with that dorque?¹

In 1964, the familiar spelling was captured in the May issue of American Speech:

The word dick itself serves as a model for two variants which are probably Midwestern, dirk and dork, also meaning “penis.”²

The sense of a contemptible person dates to at least 1967. From Don Moser’s and Jerry Cohen’s The Pied Piper of Tucson of that year:

I didn’t have any clothes and I had short hair and looked like a dork. Girls wouldn’t go out with me.³

Some contend, incorrectly, that dork originally meant a whale’s penis. That’s only half right; there is nothing particularly cetacean about the word.

¹Historical Dictionary of American Slang, v. 1, A-G, edited by Jonathan Lighter (New York: Random House, 1994), 638.

²Lawrence Poston, “Some Problems in the Study of Campus Slang,” American Speech 39, no. 2 (May 1964): 118.

³HDAS, v. 1, 638.