The first poster John Gilroy did for Guinness is believed to be of a seal balancing a pint of beer. Gilroy apparently got the idea while visiting the circus. The UK Independent related the story last year, when Guinness was celebrating their 250th anniversary, and simultaneously their 80th anniversary of advertising.
The artist was reputedly visiting the circus one day when he was impressed by the sight of a sea lion balancing a ball on his nose. Gilroy, deploying the strange thought processes of great advertising creatives down the decades, conjured the image of a sea lion balancing a bottle of the black stuff and made it the subject of an iconic Guinness poster ad. From there followed a menagerie: an ostrich, a tortoise and then the famous toucan, the best-known Guinness animal.
That would have been in 1930, the year after Guinness began advertising. Gilroy continued to work on this Guinness campaign for the next 35 years.