Dick, as you probably know, is not only slang for "penis", but also a
nickname for "Richard", a common male name in English.
From 1553 onwards, we can see refereces to "dick" as a "fellow/lad".
It probably existed beforehand: " and so most of the slang senses are
probably very old, but naturally hard to find in the surviving
records. " (Online Etymology Dictionary, "dick",
The first evidence of "dick" as referring to a penis is from 1891, in
British army slang. (ibid).
Cecil Adams, "What came first, Dick or "dick"?", The Straight Dope,
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