Here are some of the names who made quite an impact on Castlevania's gameplay history:
arukado: A pioneer in low kill games and low percentage runs. He perfected many of the glitch techs used in those types of challenges, like the revenge tech. Arukado also found the last known glitch room for SotN; using outofthegamer's mist-up tech to raise SotN's percentage to 425.5%.
Bug7139: The god of glitching. The "bug" of Castlevania gaming. Possesses excellent gameplay skills on the emulator.
machinegun: most obviously the best Lament of innocence player on the internet. Has the fastest Crazy Mode bossrush record which is even faster than the current online normal mode bossrush.
megamanneo(not sure how to spell name): discovered the "axegasm" for Portrait of Ruin (not 100% sure on this, needs correcting?).
Morgoth Galaxius: Possibly the most famous of old school glitchers. He has found glitches for almost all Castlevania games from Castlevania 2 to Symphony of the Night. Morgoth discovered the DHR (double heart refresh) tech and was one of the earliest testers of the famous Wolf Glitch.
outofthegamer: A talented game glitcher. outofthegamer waited until the great percentage hunt of SotN began to come to a halt, before making his presence known to the other glitchers online. Then the percentage went from 396.6% to 425.5%. With discoveries like S4R (shift 4 rooms), Mist-up, and the 3rd invisible room in the IC Keep - which led to Bug7139's discovery of the IC Keep Death Tech. outofthegamer also pioneered glitch techs for Aria of Sorrow, reaching an all time high of 299.0%. And possibly the highest percentage ever recorded in Dawn of Sorrow, 321.8%. The console Castlevania, Curse of Darkness, was not safe from outofthegamer's touch either. He found ways to get outside the normal game area with Hector and Trevor!
Paledim: One of the earliest known glitchers of SotN. Pale-Dim found many of the first glitch rooms, and helped Morgoth Galaxius develop DHR (double heart refresh) into the uber-glitch tech that it became. This paved the way for such glitchers as Bug7139 and outofthegamer. Pale-Dim also started the first Castlevania Glitcher Forum, World Beyond Walls.
Persona: was one of the few who has made Castlevania speedrunning as popular as it is to this today with records of odd achievements such as full map speedrunning and actually being one of the few to actually have a released video of Castlevania speedruns when speedruns for console games started to become popular. Enjoys bossrushes although most of Persona's achievements comes from default mode gameplay. Made a site dedicated to Castlevania gameplay but is now closed.
Satoryu: although has started late in the Castlevania gaming, Satoryu is one of the few who can catch up with oldschool players in skill within a very short period of time. Can also perform certain maneuvers such as Alucard's (Symphony of the Night) shield backdashing legitely where most (if not all people) cannot perform (or cannot perform as well). The "future" of Castlevania speedrunning.
Serris: although does not make videos of achievements or glitches, Serris makes up for it with great planning (routes, bosses, etc). The "scientist" of Castlevania gaming.
StuckInAPlate: although barely participating in Castlevania discussion, StuckInAPlate does very well in the little that he does. Has the current fastest Dawn of Sorrow Soma bossrush record along with the fastest Portrait of Ruin Richter/Maria bossrush 2 record.
Symbolic: The only glitcher to ever achieve the 0 kill complete game on the US version of SotN. Using a 1 HR edge travel or FSET (front slide edge travel) to reach the mist relic. One of a very small group to ever pull off a 1 HR ET! SymboliC is also very knowledgable when it comes to Castlevania, he wrote the 1-beat FAQ and an FAQ for Dracula X: Chronicles.
zggzdydp: excels at GBA Castlevania knowledge. An expert at tool assisting. The "GBA encyclopedia" of Castlevania gaming.