- the most annoying robot in the worldTM
Johnny is probably the fictional character who most succinctly represents the Eighties. He appeals to the decade's sense of consumerism - he is the protagonist of the movie, but only as a secondary role to being a cool toy (I bet they designed the toy line first, as usual). His origins stem from the Cold War advancement of military technology (to his creators, his most important feature seems not to be his capability to attain sentience through a mere fluke, but his astronomical monetary value).
He represents excess, artificiality, mass production (hence the name), but also sappy sentimentality. He's also a corporate whore (scoping out Dr. Pepper signs to "test" his vision in the first flick, and sporting a Nike tick in the second). He finally solves his problems (IIRC) by resorting to violence, limiting the impact of his learning about "feelings" and "mortality" earlier on. Or something.
Most important of all, he had 500 megabytes of memory! I mean, whoa! Not in my lifetime dude!