Began being used as such around 1890 - 95, derived from the given name. Basically just as a humorous nickname for the penis.

This is the best I can come up with at the moment. In 1776, delegate John Dickinson of Pennsylvania opposed to the separation from Britain. People would say, "Don't be a Dick." I'm not sure how it began to reference a penis. EDIT: From 1553 onwards, we can see refereces to "dick" as a "fellow/lad". Obviously the name came first. The name Richard is very old, although its origin is disputed. Old English had Richeard, from Ric (ruler) and heard (hard); French had Richart, and Old German had Ricohard. The name Richer was also fairly common until the 13th Century or thereabouts. In those days, manuscripts, letters, grocery lists, and everything else was written by hand; it was therefore common and easier to use agreed-upon abbreviations. "Rich." was used for "Richer" and "Ric." for "Richard" or "Ricard." Richard and Ricard were equally popular in the Middle Ages, and the abbreviations led naturally to diminutives--such as Rich, Richie, Rick, and Ricket. Rhyming nicknames were also fairly common in the 12th and 13th centuries, and so we also have Hitch from Rich, Hick and Dick from Rick, and Hicket from Ricket. Some of these later became surnames or parts of surnames. We note that while Dick endures as a nickname, "Hick" has thankfully become obsolete, except when tied to "Dick" in rhymes such as "Hickory, Dickory, Dock." In the 13th and 14th centuries, "Hick" evolved, however improbably, into "Hudde," from which derives surnames such as "Hudson." W. Bardsley's masterful work, Dictionary of English and Welsh Surnames (1901) cites a Latin manuscript that mentions "Ricardus dictus Hudde de Walkden." Back at the ranch, Dick and Hick were among the earliest of the rhyming nicknames, first appearing in writing around 1220. Other rhyming nicknames include Polly from Molly, Bob from Rob (from Robert), Bill from Will (from William); and Hodge from Roger. The name Dick (like the name Jack) was used colloquially to mean a man or everyman. The expression "every Tom, Dick, or Harry" attests to the this as a long-established usage; Shakespeare uses "every Tom, Dick, or Francis" in Henry IV Part I. From the usage of Dick to mean average person, other usages appeared. Many other usages. The Oxford English Dictionary cites a dick as meaning a type of hard cheese in 1847, which lead to the usage of "spotted dick" (to be dealt with in an upcoming Staff Report.) The term "dick" was also used to mean a riding whip, an apron, the mound around a ditch, and an abbreviation for "dictionary" around 1860. Dick also meant a declaration, in which sense the OED cites someone writing in 1878 "I'd take my dying dick" to mean "I'd swear a dying declaration." The term "dick" came to mean policeman around 1908, and then detective. And we finally get to where you started. The use of "dick" as coarse slang for penis first arises around 1890. Tracking the history of uncouth words is not easy, since such expressions were not generally written down. How "dick" came to be associated with penis is not known, although the riding whip may have pointed the way. http://www.straightdope.com/mailbag/mdick.html

It was a phrase coined by a man in Colonial days, named Dickey McDickerton. He was a big dick. 6'6" 300 lbs. One might even describe him as being "long". Dickey was known to be hard headed. (hence the term dickhead.) He had a lesser known cousin named Cocky McCockerton. His massive member banged against his knees as he walked. The women in town couldn't help notice. Legend has it, that's where the phrase "cock of the walk" comes from. Source: Dikipedia .......M'Lady

OK, so I did some research on this one because I have no idea. Back in the day, Richard was one of the most common names. Richard got shortened to Rick, and Rick turned into Dick. Dick became a sort of "everyman" thing, and sometime around the 1890s some British Army people coined the term dick to mean penis. Crazy stuff.

I had no clue on where the work came from, have done some research and came with the same as specified by "SoDifficult", thus I will stay with said definition. Best regards.

No you have to understand that it was originally called a "Richard."

In the 1700's a tongue-tied Princess told the Knight, as she was spreading here legs, " Dick it here ".

Let’s back track. The earlier nickname for the male member is a cock, because of the back and forth movement during intercourse which is said to resemble a male chicken strutting about. The arabic word for rooster or male chicken is “deek”. Which must have been turned into “dick” as the years went by. None of this is proven as the origins of these slang words are very difficult to trace.