phrase

[chappazhead]

the phrase happy as larry, who the hell is larry??

[Aquagility]

Larry, the Lamb?

[Octavius]

Some suggestions here:

http://www.worldwidewords.org/qa/qa-lar1.htm

[markja]

look over there. see the bloke looking all cheerful? well he's larry!!!

[Sea Devil]

Most likely to be an Australian or New Zealand expression.
The earliest printed reference currently known is from the New Zealand writer G.L. Meredith, dating from around 1875:

"We would be as happy as Larry if it were not for the rats".

There are two commonly repeated contenders for the derivation. One is that it refers to the Australian boxer Larry Foley (1847-1917). Foley was a successful boxer who never lost a fight. He retired at 32 & collected a purse of �1,000 for his final fight. So, we can expect that he was known to be happy with his lot in the 1870's - just when the phrase is first cited.

The alternative explanation is that it relates to the Cornish & later Australian/New Zealand slang term larrikin, meaning a rough type or hooligan, i.e. one predisposed to larking about. Larrikin is also a term that Meredith would have known.

Hope that clears up who the hell Larry is/was.