A successful assassin would not be famous enough to be a major lore character due to the nature of their profession.
Ehh....not in a story telling sense.
Usually their stories are told one of a few ways:
1) From the PoV of the assassin...in which case you are playing the person...so that wouldnt work as a major WoW lore char (i.e. you cant roll Varian, even though you can roll a warrior)
2) From an "insider" perspective. I.e. the fellow assassin. Afterall if you yourself are privy to all the dealings in the "underworld" you might know of assassins that stay hidden from others.
3) Ally perspective. As in, you meet the big wig assassins on your side of the conflict and aid them every now and then with their missions, or at least encounter them at points as you progress through the story.
Doesnt mean you can NEVER see or hear of the good assassins.
Now as for rogues in general.....that depends on how you define who is a rogue.
If you take rogue as strictly ninja/assassins, you arent going to find many major lore chars who fit the bill imo. If you take it in a more broad "outside the law" kid of guy, you get a bit more people you can point to.
Imo, I dont think any major lore char screams rogue.
For instance if you ask someone who just has moderate interest in WoW lore, someone who plays WoW, reads the major quest plots, follows the main story and may dive into a few detailed bits here and there about the background of the main figures....
Ask them who are some famous paladins and they can probably tell you a few
Ask them about shamans, again you get a few (THRALL!!!!)
Ask them about warriors? Varian
Hunters? Rexxar, Sylvannas
Death Knights? ARTHAS!!!!!!
Mage? Soooo many to name here...
Priests? Valen and Anduin most recently
Warlocks? Again just like mages there are quite a few
Monks are a really recent addition so not many major lore chars for them yet, But even they have Chen
I think one of the reasons for low rogue pop (one of MANY mind you) is just this fact.....there are not really any notable Lore chars that scream out rogue.
Maive is close.....but if you ask a person who she mosts represents I think you will get a good amount to say warrior as well as rogue.
Garona is one..but again I doubt most people will know who she is
Then you have the VanCleefs who are not THAT major of lore chars, in the sense that again a person with moderate interests will know how they connect with the plot
Then you have Mathias Shaw...but again unless you play an ally AND a rogue you likely wont know who he is or what he does really.
I am not saying its a big major problem....just something I have noticed. No many people can rattle off a list of influential and important rogue figures like they can Mages, Locks, or Warriors.
Boy....I didnt mean for this to be so long lol