“We have met the enemy and he is us.”
This is derived from the famous statement of Commodore Oliver Hazard Perry on the "War of 1812": "We have met the enemy and they are ours". It appeared in a "modern day" poster for the first Earth Day in April 1970, and next in the comic strip itself in August 1970 in Porky Pine's mouth, and was re-used by Kelly in a subsequent Earth Day poster (1971), and further strips and in the title of the book Pogo : We Have Met the Enemy and He Is Us (1972).
A similar statement was actually used by Kelly many years earlier in his introduction http://www.igopogo.com/we_have_met.htm to The Pogo Papers (1953) which he closes with these comments:
:Traces of nobility, gentleness and courage persist in all people, do what we will to stamp out the trend. So, too, do those characteristics which are ugly. It is just unfortunate that in the clumsy hands of a cartoonist all traits become ridiculous, leading to a certain amount of self-conscious expostulation and the desire to join battle.
There is no need to sally forth, for it remains true that those things which make us human are, curiously enough, always close at hand. Resolve then, that on this very ground, with small flags waving and tinny blast on tiny trumpets, we shall meet the enemy, and not only may he be ours, he may be us.
:::Forward!
Pogo comic strip (1948 - 1975), Pogo