Main Entry: yikes
Pronunciation: 'yIks
Function: interjection
Etymology: probably alteration of yoicks
Date: 1957
-- used to express fear or astonishment
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=yikes

I looked it up because I thought that it had been around for a while. I think it was one of those words that used to be popular in comic strips like the Dennis the Menace which I read in the seventies.

Then I found this:

Yikes - this is scary - it looks like your Dennis the Menace was blonde! (actually, I should have said the US DtM)
http://www.kingfeatures.com/pressrm/rel_24_28_2_2001.htm (first appearance March 12th 1951)

Here is the one that I grew up with:
http://www.guardian.co.uk/netnotes/article/0,6729,451808,00.html (first appearance "mid March 1951")

What a terrible shock - do you mean that there is more than one?! Sadly, the US site talks about world wide syndication, so I guess that one is the original. It suddenly makes the thought of alternative life forms elsewhere in the galaxy seem more possible.

Post Edit:

There is a God. I found this explanation:
DENNIS THE MENACE
Original Medium: Comic books
Published by: D.C. Thomson
First Appeared: 1951
Creator: David Law
In one of the oddest coincidences in the history of English-language comics (far surpassing the introduction of two groups of outcast superheroes with wheelchair-bound leaders (Doom Patrol and X-Men) during a three-month period in 1963), two characters named Dennis the Menace started simultaneously on opposite sides of the Atlantic. The American Dennis began syndication on March 12, 1951. The other first appeared in The Beano #452 (March 17, 1951), a very long-running humorous comic book published each week in Great Britain by D.C. Thomson. Because each Beano issue, dated Saturday, went on sale the previous Monday, the two actually debuted on the very same day!

This Dennis the Menace was created by David Law, who went on to draw over a thousand of the feature's weekly episodes — nearly two decades of Dennis — before his death in 1970. Law's work also appeared in The Beezer, The Topper and other Thomson offerings. Two years after introducing Dennis, Law tried to emulate his own success with a feature called "Beryl the Peril", but this one wasn't nearly as long-lived.

Dennis was joined in 1968 by a dog (Abyssinian wire-haired tripe hound, to be exact) named Gnasher, in '79 by a pig named Rasher, and in '98 by a baby sister named Bea. Gnasher, by the way, looks just like Dennis's distinctively-shaped hair, but with eyes, nose and especially teeth (which can bite through granite) added. In 1986, Gnasher disappeared for eight weeks, then came back with seven puppies — Gnatasha, Gnaomi, Gnanette, Gnorma, Gnorah, Gnancy and (Gnasher's favorite) Gnipper (usually referred to as "Gnaughty Gnipper").

The British Dennis is far more of a menace than his American namesake. The latter is just a high-spirited young kid, who frequently finds himself in trouble without ever meaning to be; whereas the former, like The Katzenjammer Kids, generally finds trouble because he goes looking for it. An especially tempting target is his neighbor, Softy Walker, whose demeanor matches those of the dweebs he hangs out with, Bertie Blenkinsop, Nervous Rex (no relation to William Van Horne's Nervous Rex) and Cuthbert Cringeworthy. Despite his obvious status as a creampuff, somehow, Softy manages to come out on top every bit as often as Li'l Bad Wolf, equally unlikely to defeat an aggressive foe, thwarts his dad's evil schemes.

The "Dennis the Menace" series was popular right from the start, and grew more so with time. He starred in annuals as early as 1956. In 1974, he ousted Biffo the Bear from the Beano cover, and has occupied that spot ever since. He has appeared in animated form on BBC since 1996. His fan club now has over 1.5 million members.

This Dennis the Menace may not be as big an international phenomenon as the other Dennis the Menace — but it's pretty clear which one is the bigger star in his country of origin.
http://www.toonopedia.com/dennisb.htm