The Advanced Study Room is on KGS longer than me and I can't
describe its early history clearly - maybe NannyOgg could help
there; I think it is on KGS at least since 2004, quite possibly
since 2002 or even earlier.

Historically, the mission of the Advanced Study Room was "to provide a
controlled environment within KGS which promotes rapid advancement in Go
between 5 kyu to low-mid dan strength (say, 4 dan), by promoting self-study of
fundamentals, and providing an environment where those fundamentals can be
further explored and refined." The focus was indeed on 5k+ players and pushing
them over the 1d boundary. While over time this mission has been somewhat
extended (and maybe diluted), I personally still feel this remains and should
remain the room's focal point.

What I know is that Usagi and Bluremi, not sure how many people
remember them nowadays (I actually really don't, except that Usagi
still comes by from time to time), were main owners of the room
in the past; back then, it probably was much more focused on group
study, people gathering in demos and studying problems and games
together.

Then, the insei-like League system has been started (probably in
early 2006???), organized mainly by Sente, with very similar class
system as there is today. Sometimes, the class winners would be
given a teaching game or KGS+ subscription prize. In late 2007,
pasky started donating a 9d-level teaching game prize regularly for
A-class winner each month; someone else started donating prizes for
B-class winner later (sorry, don't remember the nick).

In Feb 2008, pasky quickly hacked together the ASR Blitz Ladder, based
on The Battlefield room engine code; then, for some months a KGS+
subscription would be given to the month winner and some people would
play more than 100 games per month in the ladder.

Unfortunately, later in 2008, Sente stopped maintaining the league and ASR
got pretty much absolutely inactive. There were few attempts to resurrect
the league (especially by derPlumps) and the ladder, but none of them
successful until CGBSpender took over at the end of summer 2009.

Some more impressions of the history can be taken from
http://senseis.xmp.net/?OldAdvancedStudyRoom