Dear 100 Hour Board,
Which past writer would you say has had the biggest impact on the current culture of the Board?
-They Call Me Tim
If I had to choose just one, I would go with the writer who first instigated the tradition of giving a silly answer to silly questions (sadly, their 'nym has now been lost to the ravages of time). As it says in our history, this was when "[the Board] was truly born."
Other than that, I feel like Katya and Laser Jock have had a huge impact on Board culture if just thanks to the sheer enormity of questions they both answered. Not counting secondary 'nyms, they collectively answered 8774 questions, which is approximately 10% of all Board questions ever. Other significant writers in shaping Board culture (in my opinion) include Uffish Thought, Dragon Lady, Rating Pending, Sky Bones, Genuine Article and Optimistic.
Prior to The Black Sheep, we didn't talk much about mental illness, faith crises, and similar issues that many BYU students face. I know she's said in the past that she really worked to make the Board a more open environment and I think that's resulted in the Board providing a very positive service to BYU students who are having a hard time.
I would like to second Anathema's nomination of Sky Bones, if for no other reason than having the most currently writing menteescendants.