Why don't I have a custom title by now!?
Dictionary: Imitator = Who did the imitation and actually created the map, imitatee = who is being imitated.
Well in my view, the key attributes of this map are:
1. It's fun and very satisfying to play and explore. However, I think this is more of a touch of the imitator instead of the one being imitated. It makes me think that the imitator is very experienced mapper specially in regards of gameplay. I guess the imitated person is someone experienced too.
2. Monsters start to attack the player immediately. I'm sure this is the first giveaway.
3. The map is compact, playable area gradiently expands and turns elaborately interconnected.
4. The mapper doesn't hesitate to use a few strange angles and little structures. The first staircase has weird angles, the waterfall staircase is obscure for itself, strange little stairs helps the player to surmount smaller height differences. Still, these structures doesn't at all spoil the map.
1. The map is broken in ZDoom. Lost souls and cacodemons don't teleport from conveyor belts. For me it gives a proof that the author (imitator) must be a dedicated PrBoom user!
2. When you look on the automap, it is... nice, and gives the impression the map was preplanned on paper before being actually started.
My first point (1.) narrows the selection range to about a half. Point (4.) excludes Essel to have anything common with this, as well as other mappers who take pride in clean design. People like Khorus and Joshy are out too, at least as imitatees, since their maps tend to be more extensive and avoid using little details just for playability reasons like it is in this map. Imitated person definitely isn't a slaughtermapper.
I'm 90% sure this map is related to Memfis. I'm just not sure whether he's the imitator or imitatee. If he was the one being imitated (the imitatee), I'd say the attempt at emulating his style wasn't that well performed. Memfis's maps tend to be less linear, don't let the player jump over/off ledges that much, he uses little stairs but they look different, and while their monster usage and difficulty is similar, higher monsters are introduced quite fast for Memfis. I can quite well imagine that Memfis is the imitator and he was imitating someone who... make (firstly) linear maps and don't mind using odd angles, platforms, obstacles in way and nontiling textures (see exit door) while in other instances he sticks to orthogonal/45-degree architecture. But then, who would it be? Or wouldn't it be kind of vice versa?
I admit I'm not familiar with works of all people involved in this project, I'm sorry. I have no idea who is imitated if the imitator is actually Memfis, and there's still possibility Memfis has nothing common with this map. My wild guess:
The person being imitated is Memfis, and imitator was fiend-o-hell (his style fits a bit my description of who would be Memfis imitating, and the style of the map anyway reminds me Memfis, so I say he's the imitatee. On the other hand, the monsters at start don't fit...)
Or vice versa, but take the first.