Preston B. Whitmore is a major character in the 41th classic Disney's movie Atlantis: The Lost Empire and its 2003. He was the best friend of Milo Tatch's grandfather.
In the movie Helga Silcari goes to visit Milo at her house late and tells him about Preston (her boss) and takes him to him terrorizing Milo with bastard jokes. When Milo meets Preston for the first time, he immediately proves friendly to him and gives him the Shepherd's Journal which was his grandfather's gift that he should have given him.
Preston jokes a little that he kissed Taddeus on the mouth for losing their bet and admits that he was really lousy.
Preston then gives Milo command of the expedition that will find the Heart of Atlantis and a submarine and introduces it to everyone before they leave.
At the end of the film, Preston is seen talking to Audry, Sweet, Moliere, Venny, Cookie and Packard making up a false story about no ancient city gimmicks and the disappearance of Rourke, Helga and Milo. In Milo's photo he finds an Atlantis diamond as a gift and a message on it.
In his 2003 sequel Preston visits Milo with his old friends for the first time in Atlantis, and also informs about something happening on the surface that they need Milo and Kida.