How do you tell a 4-year-old who the Buddha was?

I'm in the process of organising a family day at my Local Buddhist Centre. I'll be taking my 4-year-old daughter with me and she will once again ask me who is the Buddha? Previously I have always given really weak answers such as 'he was a very nice man who lived a long time ago'. Not very satisfying to anyone. So what would be an age appropriate way to describe who the Buddha is? I want the description to be accurate and accessible to her. Obviously the more complete the better but realistically things are going to be left out. Also I don't want to slip into using Christian type words for Buddhist concepts - for instance not using heaven for nirvana, church for sangha etc... So what would be a good way to describe who the Buddha is to her. I'll be honest I think I want a Dr Phil script of the month type answer for this. Many Thanks for all/any help on this one.