I never heard of this guy before, apparently it's a US celeb. The car itself has come up a few times before. You can find quite a bit about it. This link contains a good overview with pictures:
Update: As I have now a little more time I checked out Dean Martin. Judging on his 400 ownership it clearly was someone with good taste. Turns out it was a Italian American. Just see his Wiki for all details: http://en.wikipedia.org/wiki/Dean_Martin
I also looked up and listned some of his songs on YouTube. Perhaps I should consider to convert some onto MP3 and play it in the 400. A while back I bought this MP3 Cassette adapter. I think this goes nicely with some Fausto Papetti songs.
And hereby also a small tribute to Dean Martin:
Update: to my surprise the Original article is removed by the post Gazette. I did some further checking and found this older article which contained nearly the same content. I almost would say the Gazette copied and pasted it ...