You have no idea how long it took me to find a copy of this. I saw one in a supermarket in about 1996 and thought "Oh I'll get that tomorrow", but I didn't find another one until this year on Australian ebay.
It has long been available on VHS in the US, ironically (since it's an Australian show), but I have no idea if that version has been redubbed with American voice actors, as often happens.
Anyway, 'Arthur' was if not the first, then one of the first Australian animated TV series. It used to be on when I was about 7 or 8, and I used to love it. I was amazed to discover after so long that it's pretty much as good as I remembered it.
The show was made by Australian animators who basically had almost no idea what they were doing, so they made it up as went along. The result is remarkably professional, and looks better than a lot of US cartoons from the same period. In fact, for years I thought it WAS American.
Obviously it's a take on the King Arthur thing. It gets compared with Rocky and Bullwinkle a lot. Let's call it a cross between Rocky and Bullwinkle and 'The Wizard of Id'.
The plots are very silly and usually involve Arthur and the good guys (Merlin, Lancelot, Guinevere) trying to foil the plots of Morgana and the Black Knight (who has a delightfully ridiculous accent, and a penchant for appearing in drag) - however threats often come in other absurd forms, such as a Mongol Emperor who wants to take the place over and fill it with elephants.
The show doesn't balk at introducing totally incongruous things like powered aircraft at times.
Arthur is voiced by the late great John Meillon, who would be known to American audiences as Walter Reilly in the Crocodile Dundee movies, but who had a long and distinguished acting career in Australia.
The animation is limited of course, but no worse than anything else from the 60's. Really it's a great show, and I had the theme song stuck in my head for about 30 years before I finally found a copy. Possibly the most important animated series in Australian TV history, and disconcertingly good after 40 years.