An interesting bit from IMDb.com:

"Val Kilmer initially accepted his role so that he could work with Marlon Brando. Before filming started Kilmer informed the production that he did not want to be involved in any capacity due to the creative direction of the film, but due to the massive success of Batman Forever (1995) the studio could not afford to let him go and he was forced to participate by contractual obligation."


Also; Val Kilmer on Inside The Actors Studio 3.13.00:

THE ISLAND OF DR. MOREAU and Brando

The first words out of Mr. Kilmer's mouth on this subject were, "Awful, boring script."


Haven't seen that bit myself before, but it makes sense. Kilmer did request a forty percent cut back for his screentime when he was to be the leading man.

Yes, it does make sense: he was pissed off and, being the balldriller many people say he is, he squashed the production until the bosses told him to pipe down (after Stanley's substitution), again by using contract obligations as support.