Green’s Dictionary of Slang

(Aus.) a fly.

1967		F.J. Hardy Billy Borker Yarns Again 2: ‘Who’s Louis the Fly?’ ‘The ringkeeper at Tommo’s Two-up School; had buck teeth like the fly in the T.V. commercials. His mates used to say to him: ‘I hate Mortein. Louis hates Mortein.’.
1980		Peter Luck This Fabulous Century 347: The ‘Louies’ we see in television commercials are actually raised in science laboratories [GAW4].
1986		Bulletin 23 Dec. 208: Samuel Taylor, manufacturer of Mortein, Aerogard and Pea-Beu, is having a series of particularly good weekends as everyone rushes to hit Louie with the old Pea-Beu. Louie, incidentally, is 30 this year.