Anyone know who the Larry is in the expression "as happy as Larry"?

It looks like no-one is really sure, but this site Larry 1 has a couple of theories.

QUOTE-There’s a suggestion that it comes from the name of the nineteenth-century Australian boxer Larry Foley (1847-1917), though why he was especially happy nobody now seems able to say.-UNQUOTE

It also may be a corruption of the word 'larrikin'.

and another theory:

happy as a clam

What's so happy about a bivalve mollusk, anyway? The reason this phrase seems nonsensical is that part of it has fallen away. The original phrase was happy as a clam at high tide--that is, when the high tide makes the critters safe from beachcombers.

happy as Larry

A less common phrase that means the same thing is happy as Larry. Its origin is uncertain, though some speculate that the Larry here is Lazarus, who was supposedly raised from the dead--and who, one assumes, would have been very happy indeed.

http://www.funwords.com/library/h.htm