A Long Forgotten Evil

After having some difficulty with this guy myself I realized I had to get a little creative. If you want to kill this guy you have to abuse LOS. There are two pillars to the right and left of this guy. All you have to do is this:
Pre fight: get out a dps pet, DON'T USE A PET WITH TAUNT, IF YOU WANT TO USE A PET WITH TAUNT, TURN IT OFF
1. Open the fight with your hardest hitting attack. (to make sure you have aggro and not your pet)
2. Immediately run behind the first right or left pillar when he begins to cast affliction
3. This will cancel his affliction cast, giving you time to jump out and put up any damage you can in to him (DOTS useful)
4. As soon as he begins casting affliction go back behind the pillar(if you're ranged you can squeeze out another second and wait till about 60%), repeat step 3 (refresh any dots you have/auto attack)
5. If he begins casting storm behind your pillar, switch pillars.
6. As long as you LOS correctly and don't let him cast an affliction on you, he wont cast any of his other spells besides storm, which simply requires you to switch to another pillar while it's casting.
THIS FIGHT REQUIRES NO INTERRUPTS, IN FACT, IF YOU HAVE AN INTERRUPT DON'T USE IT BECAUSE IT WILL CAUSE HIM TO CAST SOMETHING OTHER THAN AFFLICTION
I FINISHED THE FIGHT AT 100% HP AND DIDN'T INTERRUPT ONCE.
If you let him cast affliction on you even once it screws everything up, so you have to stop it every time.

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EDIT: I haven't done this fight as a melee, only ranged, so for melee you might need to stay behind the pilar long enough for him to run over to it so you don't have to run as far to LOS him, also, for those that don't know LOS means "line of sight" which basically means putting an object between yourself and your target.

Have a little suggestion for those who play juggernauts.
As I am typing this, I just finished this mission...and here is what I did.
I took Teser's suggestions as a general rule of thumb, but instead did the following that actually worked the 2nd time around:
1. Break Quinn to keep the heals on you
2. Go into Soresu Form and put Guard on Quinn
3. Force charge and interrupt the first Affliction
4. Run around the room and you will see that Quinn will dps the boss AND heal you as well.
5. You will take some damage, but if you get close to the boss, drop as much dps as you can like Force Scream/Sundering Armor and anything with an instant cast.
6. Don't forget to use Shield Ward / Call of the Force / medpacks and Endure Pain

I was kind of shocked that I completed this, but as messy as this tactic is...it worked.

P.S. Being melee in this fight was crappy

This fight went best for me when I had my companion go down early one attempt.

As a Operative (Medicine) I couldn't keep any of my companions up long enough. Finally, after SCORPIO went down really early one attempt I tried much more LoS. Worked like a charm. At least as an operative, get rid of your companion. Use the closest few pillars to LoS. Move to a different pillar when he uses force storm. Every time he starts casting, duck behind one. Step out when he's done and use dart, blaster shots, etc. Might take awhile, but in the end it was easy.

Sith Marauder:

If you're using Jaesa, stop. Put Quinn on for this one fight, even if he's still in his crappy level 20-32 armour.

1. Force Charge. If he starts casting affliction, disrupt it with disruption.
2. Quinn will probably have frozen him either before or after that. If not, just run for a pillar anyway.

BIGGEST RULE: Always keep a pillar between you and the Avatar. Even if it means running around in circles.
Rule #2: If you see the blue target on the floor near the pillar you're on, change pillars.
Rule #3: To keep aggro, every time Quinn freezes the Avatar, Force Charge & run off.

You can disrupt the Affliction with Force Choke, too... but best not to do it on the first one. If you get in a situation where you're not going to be covered in time for the affliction, use force choke.

As an operative Medicine i used Lokin as compagnion. This worked ery well in combination with LOS tactic.

Started with a hidden strike
Interupted the 1st afflication
Used mainly corrosive dart and the dps of lokin to get him killed

Ok took a while (like 5 minutes) but he is begging for mercy now :)

As an IA Operative, I too died a couple times to this guy, using DPS companions. They died almost instantly.

I fared much better when I used, surprisingly, Dr. Lokin.

I used LoS tactics, moving myself around the pillars at the top of the steps every time I saw the enemy start to cast something. Lokin kept me healed up pretty well, supplementing my own heals, and he didnt draw aggro. He also throws out his carbonizing spray several times, so I could pop out and dps the mob down in longer spurts, and even get in the occasional backstab. Most of the time my DPS was limited to blaster fire, Corrosive Dart, and Fragmentation Grenade, and a couple Explosive Probes when Lokin sprayed him. Finished the fight with Lokin and I both at full health.

This fight wouldn't be too difficult if your companions actually responded when you told them to. As-is, if they're standing in an AoE effect, the most you can do is temporarily switch them to passive, let them move to you, and switch back to attack again. Not only does this distract from your own spells and movement, their response times are fairly delayed while doing so - so odds are, you're both going to eat a lot of damage if you try it.

As another poster said, you don't have to interrupt the spells - you can LoS them, if you clear out the area beforehand.

I ended up getting even more cheesy with my strategy (playing SI). My companions died in seconds, even when I healed them (and I'm sorc, full corruption spec). So I just DoTted up the boss, stunned him with Electrocute, knocked him back with Overload, popped Force Speed whenever available, and kept Resurgence rolling on myself, refreshing Static Barrier whenever possible. Basically... I kited him. All over the entire tunnel (he doesn't leash). If you make use of pillars, corners, and other obstacles, you should be able to get a casted (non-HoT) heal or two off on yourself.

Just keep applying DoTs and keep moving. If you can LoS or interrupt his casts (or move out of the way of ground-targeting effects), you should be okay. You might feel dirty for cheesing the fight out, but you should be okay.

Just finished this quest, basically like everyone stated, its more of a brain fight rather than brawn

Took all the comments and basically just spun around pillars to avoid affliction, switched for force storm.

Used Jaesa for my companion, did a minor dps dump then started los'ing before she went down. For my strat tho, i had to make sure i had to interrupt the first few afflictions. Reason being is that i had to bring him beside the pillar in order to do a "circle-around" method. Didn't want to risk aggro pulls by Jaesa so i had to guarantee the transition to the pillars myself. Combinations of int roar, force choke, force push and disruption should lead you to the lower left (or right) side of the platform (if your looking at it from the top PoV). The trick here is to actually be on the opposite side of the pillar as him, and dps'ing him only when he has a long cast -- meaning you have to dps then hide back in at the pillar. You can try to circle him out, land a couple of sunders but ensuring you wouldn't be in the LoS once the cast goes off. Force Scream seem to work well, while impale does the trick when switching over to the other pillar. Think of it as going in an "8". There will be occasional damage though, but nothing you couldn't tank out. Did this is Shien form for the extra damage.

Also, make sure you don't fall of while LoS'ing. That's gonna hurt.

Other than that, a fun fight. Should take a couple of tries for some juggs to get the hang of it but once you get it, its cake.

"Another horribly designed, impossible quest skipped due to Bioware's incompetence and inability to design quests properly."

This is not WoW. You are actually forced to learn how to play your class in this game as you quest alone, and not spam buttons. I did this as a lvl 47 Merc, with Mako. Did I do it first try? No. Did I do it 2nd or 3rd? No, But I came back about an hour later after thinking it out and when done correctly it is cake! I have not found a quest I have had to skip yet.

"This fight needs a ton of interrupting and Merc Bounty hunter doesn't have one nor can any of the companions do one. GG BIOWARE!"

Really? Merc BH has Electro Dart as an interrupt and even in emergency situations Concussion Missile can be used if you need a quick heal on yourself and not let it last too long. Mako also has a pretty decent interrupt that when it goes off is a great time to throw a heal on yourself.

Mercenary with bodyguard spec. Did this fight about 10 times before succeeding.

Tried first with Blizz, failed 4 times. Couldnt keep up the healing on my trusty tank. Only managed to get boss to 60-70% each time.

Tried again with Gault, range DPS. At this point, tried kiting boss within his area. Failed 2 times. But can bring him down to around 50%-60%. Read up and saw people used LOS, so tried doing so but still failed twice.

Ended up using Mako, kiting the boss all over the tunnels. first try failed, but did get boss to around 30%. Disabled all attack abilities on Mako and left only the healing ones + her stun ability. Tried again and managed it after 5 mins. Used 2 med pacs, but was well worth it!

46 Sith Jugg Veng spec w/ Vette.

Pain in the ass for melee's as the first 2 times I tried he just ROCKED me hard.

Pulled with saber throw and taunt while vette started DPS
Hid behind one of the broken columns on the right until his affliction was finished casting where it didnt go off and he started casting other things.
From there it was a matter of having vette just continually dps him while I jumped in front of and behind the columns.
When the AOE came down, I went to another one. He ran over a few times to where I would force scream, impale and shatter depending on how much time I had.

Few times he targetted Vette I would just taunt and hit him once before heading back to LOS him. Had to force push him away because of the aoe storm once and had to use a medpac, but didnt use saber ward, CotF or Endure Pain.

Poor guy, the game actually poses a challenge and requires you to use that brain of yours, and you go crying about it?

There are plenty of things you can do to prepare for this fight, go buy some Medpacks and Stimpacks if you dont have any, pick the best Companion for the job and make sure that companion is well geared.
As stated before, use the pillars to your advantage to dodge some of the spells he casts, and be sure to use any interupts you have wisely.
The fight is not difficult once you prepare for it and use a few tactical elements, which i dont think is too much to ask of a player.

I for one, applaud BioWare for making some of the missions reasonably challenging, they are not at all impossible - it just requires that you actually use your brain and think out some strategies to use and not just breeze through it like you do in most "no brainer" mmos like World of Warcraft these days.
Most of the missions are a piece of cake anyway, so really, dont you think complaining about there being a slight challenge in a few of them is a bit over the top?
Or maybe i am just old fashioned, and dont like everything in a game being served to me on a silver plate and not require any thought activity on my part.

A shame, i bet that the game will be converted to "easymode" once they get enough of whining kids that dont understand why they have to use their brain while playing a game.

as a marauder i got the ultrachrome boots as a reward:

either:
http://www.torhead.com/item/4yfe82W/ablative-ultrachrome-boots
or
http://www.torhead.com/item/eSgNVNu/hardened-ultrachrome-boots

without an aug slot though.
(and a class 5 lockbox and a voss commendation)

I have no DoTs. The pillar thing doesn't work and he just follows me around and I don't have enough time to get to it even using force run before he casts spells on me.

Another horribly designed, impossible quest skipped due to Bioware's incompetence and inability to design quests properly.