Today I was reading the official rules for the Legacy challenge, and in the Nightlife EP rules, it mentions something about marrying Mr. Big or The Diva.
I've been simming for nearly three years now, and I've never once come across either of these characters...does anyone have any info about them?

Thank you!

http://sims.wikia.com/wiki/Diva

This game can be strange at times, you've never seen her at all thehoff2, but my game seems to have two of them!
One of my university Sims befriended who I thought was the Diva ... she has the same hairstyle, same black dress, does the Primp action constantly. It wasn't until his housemate threw a party, both the original Diva and this other one who is like a clone were there, that I realised I had two identical Diva's in the game.
Hope this isn't a bad sign and my neighbourhoods about to go up in smoke?

you can access the diva or Mr big by typing testingcheatsenabled true right click on the mail box and chose them as visitor they will then arive on your lot and you can befriend them and marry them which will add 70.000 to household funds,once one diva gets married the game will generate another one.I have 3 divas now.The children of divas as I have noticed copy the pimp action

The link"Prosthetics" gave you is good, But I will add my two cent ( lol )The Diva and Mr. Big are potentially lucrative but difficult dating challenges. If you manage to marry/ join them with one of your sims their fortune and top level icome become a part of your household, getting there can be difficult because they are both "VERY VAIN" and very picky. The name Mr. Big and Diva is refer to them as characters. In the game they are given "Unigue" first and last name.

Also you will notice in the clothes buying catalog you always see the Diva dress in the color "Black" for other female sims that dress is just in the color red for other sims, only the Diva have the black color dress this goes for Mr. Big as well there are other colors for the male sims like his outfix but they can not get Mr. Big color red. They hang downtown a lot ( try to get your sims to talk to them ) once they are listed in the sims phone list you can called them and build up the relationship from there, and invite them over. Now if they will fall for the sims depends on the Diva and Mr. Big. lol I have had Mr. Big join in a household in the past, Once he join the game will make another Mr. Big ( also The Mr. Big who join the household will still keep his Vain personality and his special outfit that he is wearing along with other clothes you may buy him. ( He was really a good father in my game and made "beautiful children", having a pretty female sims help with that as well lol ) Most of the Mr. Big are very handsome ( well in my game they are lol )

I never really wanted to add the Diva to a household all those she fell for one of my sims, because to me she look to hard looking in the face Maxis should have made her have more of a softness in the face. Most of what I tell you here about the characters and the way they are. I read in my "Official Game Guide NightLife book" that I read so long ago when NL first came out. A lot of stuff you will find out on your own when playing them. One thing I hate about them is when they come to visit a sim or anything else they will whip out their "Mirror" to look at themself they are Very, Very, Vain. They do act like they are the Kings and Queens of all sims. hahaha :D

Well well well you learn something new everyday. I had no idea that those two Sims were more "challenging" to woo than others. I recognize them by their descriptions but since I tend to only have Romance Sims interact with townies in any way other than friendly I never had either of them move in with a Sim.

Hmmmmm 70,000 simoleons however is a bit of an incentive. Can always have them move out afterwards. Bwahahahahahaha!

First off, that typo made my day xD

And second, thank you everyone :D
After reading the article on the other end of the link prosthetics gave me (I'd never even heard of that site before, but it's incredible, so thank you for that, too), I realized that once, a year or two ago, I got one of my sims to marry Mr. Big. I'd always wondered why he loved himself so much...

Again, thank you!