The character is Gordon Freeman, the protagonist for the game series Half Life which is the game Valve is best known for.

The Lambda here represents the radioactive decay constant and is used as part of the measure for the "half life" of any radioactive material.

The Gordon character is a scientist, much of the game is set in a science lab and Valve are known for making games with many scientific references (see also: Portal).

I can't really tell you. That guy is "Gordon Freeman", the main character in the Half-Life game serie. According to the following article, it comes from the "Lambda complex" where he's working on in the first serie, which is in also made-up for the game: http://half-life.wikia.com/wiki/Lambda_logo

neither. its gordon freeman(1) from half life(2)

1: http://en.wikipedia.org/wiki/Gordon_Freeman 2: http://en.wikipedia.org/wiki/Half-Life_(series)

I suddenly feel very old :(

Edit: unless you're not a gamer (yes, I'm clutching at straws!)

It's Gordon Freeman, the main protagonist from the Half Life series.