Hanks, ScarJo set for Letterman's final 28 shows

It's David Letterman's 28 evening-long victory lap.

The legendary late-night comedian signs off for good on May 20.

And he's doing so with the help of some of Hollywood's finest, beginning today.

We're talking Alec Baldwin, George Clooney, Billy Crystal, Robert Downey Jr., Will Ferrell, Tina Fey, Michael J. Fox, Tom Hanks, Scarlett Johansson, Steve Martin, Bill Murray, Sarah Jessica Parker and, of course, Oprah Winfrey.

Letterman will make nice with the always-affable Parker and 2015 Masters champion Jordan Spieth on Monday; Billy Crystal swings by on Tuesday; Michael J. Fox on Wednesday; Kevin James on Thursday; and Alec Baldwin and musical guest John Mayer cap off the week on Friday.

For celebrities making the talk-show rounds to promote a book or movie or TV show, a stop at Letterman's frigid studio at the Ed Sullivan Theater was more than just a rote burden. You can't just phone it in, or Letterman will bust you.

"With him, you never know what to expect. Jay Leno was the complete opposite. Jay would come in and greet every guest. You don't see Letterman. There's none of that," said Mark Wahlberg.

Letterman has been responsible for some of pop culture's most talked-about moments: The time Drew Barrymore flashed him in 1995, that unforgettable Joaquin Phoenix bit of performance art in which he acted like a rancid and confused version of himself, and of course, that time he confessed, on air in 2009, that he'd had affairs.

Stephen Colbert takes over for Letterman this fall.