Well, you might think this has already been answered, but apparently wrongly.
As HOL is also interested in handles of sceners who went on writing commercial games (e. g. Pinball Dreams / TSL), these infos MUST be correct.
After some research, I'd say it's Stefan Boberg
indeed, although Galahad was saying this is wrong
and "correcting" (?) it to 'Andreas Tadic' in an ancient thread and also in the 2002 "Weekly King of the Scene Competition I"
on EAB. Well, Galahad was IN-DEPTH of the scene, so you really need a lot of disproving material to say he's wrong...
BTW, I remembered this thing because someone mentioned Superfrog, which was programmed by Tadic.
I WANT to get this mystery solved and prove Galahad wrong that Antiaction is NOT Tadic. It's almost improbable he is because I found so many disproving infos.
Antiaction went through a variety of groups, one was TETRAGON:
Tetragon was a swedish group. The four best members (JBM, Trigon, Joker and
Hater) joined Dual Crew around 07/90. Swedish coder Antiaction (responsible
for the famous Tetra-Packer) then joined D-Mob.
(source: Scenery Amiga
I'm 99.99% sure that Tetra-Packer was programmed by Boberg
( = Antiaction!), who also did LHA.
Tadic was in Phenomena and Triangle, according to my researches.
found neither Tadic nor a certain "Megaman", so he might have gone under the handle "Dream Warrior"
link holds a couple of interviews with sceners, which have Antiaction and Tadic in SEPARATE lines, so this gives the impression that they are NOT the same person! Moreover, what they say is completely diverse.
This should be enough to disprove the assertion that Antiaction = Tadic.