I guess as others have said, it started with RFC.
For me the first I can think of is when I solo the spider in BRD for the T0.5 set pieces, I had to kite the spider over an edge, shoot one starfire run and jump up a ledge and shoot another starfire and keep doing that for 30min Later in TBC I soloed Hellfire Ramparts heroic as tank feral, and later on i remember solo Anzu in Sethekk halls HC for the mount. Fun times then you think back im time.