Here is a discussion about characters in advertising and what makes them effective.
The author argues that characters can be difficult to evaluate when initially putting them in front of consumers because it is easy for people to dismiss them as childish or silly. However, some really bizarre characters (The Most Interesting Man in the World for Dos Equis and the Geico Gecko) have been very successful.
Many successful characters are archetypal representations of what the brand represents (Betty Crocker) others demonstrate how the brand works in a symbolic way (The Pillsbury Doughboy, The Energizer Bunny). But what else makes a for a successful character?