Dead celebrities can make a lot of money. Technology is advanced enough to make it so the celebrities' image and likeness can be made to appear alive on film. Holograms can even be used to make it appear that a deceased person is performing on stage at a theater.
For the estates that hold the rights to the likenesses of celebrities this can earn millions of dollars a year. Such is the case with the likenesses of Michael Jackson, James Dean, Betty Page and many others.
Not every celebrity, however, is comfortable with the idea of their name and likeness being used after they pass away to make money.
That appears to have been the case for Robin Williams.
Forbes reports that a trust agreement bars Williams' name or likeness from being used for 25 years in an article entitled "Why Robin Williams Won't Be Making Millions Beyond The Grave."
As the article points out, many celebrities might consider doing the same thing as Williams to avoid complicated tax issues.
However, in Williams' case there was no need to limit the use of his name and likeness for tax purposes as the rights to use his name and likeness are held by a charitable foundation.
Apparently, Williams was uncomfortable with the idea of someone else deciding how his name and likeness could be used in the years shortly after his death. For example, he may not have wanted someone else deciding that he should endorse a product that he himself would not have.
Reference: Forbes (October 27, 2015) "Why Robin Williams Won't Be Making Millions Beyond The Grave."