Well, it certainly took a long time, but it looks as though the Nate Robinson deal has finally been completed, according to The Boston Globe:
The Celtics are waiting for NBA approval and the deal may not be announced until later this afternoon.
So who exactly is Marcus Landry? He's a 6'7 rookie out of Wisconsin. Beyond that, I really can't tell you a whole lot. You've probably heard of his brother, Carl Landry, who was actually traded to the Sacramento Kings earlier today. Here are some links to help you get acquainted:
Jessica Camerato of WEEI also has a short profile on Landry.