If I'm making a big movie I make sure that I check to see if any of these guys are available. Castable to me is a combination of past success and current popularity. There are stacks of popular actors without a good resume eg. Zac Efron, Megan Fox, Ashton Kutcher, Blake Lively and then there are actors with a good resume who aren't particularly popular at present eg. Morgan Freeman, Ewan McGregor, Kevin Spacey, John Travolta.