Definition of the Thrommel-Fragarach problem
Perceptive readers of the Temple of Elemental Evil module [T1-4] would come up with the following question:

How is it possible Prince Thrommel of Furyondy, a Paladin Lord, to be the wielder of Fragarach, a Chaotic Good alignment broad sword??

Extreme 1: Fragarach is actually Lawful Good
This extreme solution is based on a Gary Gygax interview by Paul Stormberg in Oerth Journal 12, entitled: Thus Spake Gary Gygax: Ye Secrets of Oerth Revealed. In this interview Gygax claims that Fragarach's alignment in T1-4 was an editorial error, and that the sword should have been designated as LG [OJ12]. Moreover, the nature of the weapon to strike unerringly back supports a lawful behavior [T1-4].

This solution works perfectly well for the World of Greyhawk campaign setting. Thrommel's missing in [T1-4] alignment and faith are easily extrapolated to be LG and Heironeous, the official religion of Furyondy. Otherwise, Thrommel could not have been the heir to the throne of Belvor [Guide].

This solution is problematic if we take into account Celtic mythology. Manannan Mac Lir forged the weapon, gave it to Lugh, and trained him to fight the Fomorians [Dr.65]. Celtic pantheon seems to include few LG deities (1), and neither Manannan nor Lugh were ever designated as LG (2). It is true that Celtic warriors in frenzy could hardly use a LG weapon.

Moreover, questions arise like how is it possible that CG Fragarach is a typo, while at the same time throughout the description of the weapon in [T1-4], this typo is repeated many times, either directly or indirectly with respect to its side effects on wielders with various alignments? Or why is Thrommel's alignment or faith omitted in [T1-4]?

Extreme 2: Thrommel is actually Chaotic Good
This extreme is based on an unconfirmed, though intriguing, communication of "Cooter Pooch" (a Troika guy?) with Gary Gygax. Throughout this communication Gygax claims exactly the opposite from what he said in the Oerth Journal interview. He states that he "was planning a CG Paladin, one who didn't fit the mold," and that "the easiest and likely more interesting way of managing the dichotomy is to have the name "Paladin" as a title."

This solution is in line with Celtic mythos, but its applicability to the World of Greyhawk is problematic. It is clear that in order to be the secular leader of the unified Veluna-Furyondy state one is expected to steadily prosecute law and order with more precision and rigor than in the case of the Kingdom of Furyondy alone [Guide]. More questions arise. Could Thrommel be this kind of candidate? Would Belvor and Hazen make any unification plans knowing that Thrommel is CG? To elaborate on this basis, one could argue that if "Paladin" is Thrommel`s title, then before a time prior to his abduction Thrommel was a real Paladin (i.e., above or equal to 9th level paladin). How did Thrommel`s alignment change happened? Obviously no one realized that he lost status or he was too powerful to be challenged after the victory at Emridy Meadows. How can we estimate the time that Thrommel`s alignment change happened? All these questions of the present and previous sections we attempt to answer in the next section.

The median: Cursed Fragarach
The most simple and convenient solution is that Fragarach is cursed. It is true that a Celtic weapon can hardly be LG (but note also that the inconsistency of alignment information on Lugh, and Mannanan gives freedom to designate Fragarach as you wish (2)). After all those years of addling and confusion, Fragarach seems to be a great plot device to plague evolved societies like the ones of Furyondy and Veluna. According to a Dangerous Journeys system source the weapon has duplication properties, and this is how 6 copies of the sword were produced [Aerth]. Every copy carries the curse. Divinations, identify, or know alignment will all reveal that the sword is LG. The curse is subtle and very hard to identify due to its non-evil nature. The paladin owner of the sword experiences a very slow alignment change, over the years, to Chaotic. During a large-scale battle of ultimate importance to the paladin, the sword manifests its true self, the alignment change of the paladin is completed, and he gets into the frenzy of the Celts. In this condition the paladin looses status, and does things he will not remember. From then on the weapon can be identified as CG, and is side effective as per [T1-4]. The above theory explains the questions asked in the previous sections plus how is it possible that the weapon was lost at the Battle of Emridy Meadows?

Thus, together with "On Thrommel's Abduction" and "Murlynd´s Early Adventures & Subsequent Ventures: The Epidemic, and Heads Down!" Thrommel`s obscurities are almost fully explored.

Footnotes
(1) The only Celtic god designated as LG in Deities & Demigods Cyclopedia, Dragon 65, and Legends & Lore is Diancecht.

(2) Alignment table for Manannan Mac Lir, and Lugh in various sources

[D&D] [Dr.65] [L&L] [Celtic] Manannan Mac Lir CN NG LN LN Lugh N N (implied) CN CG

References
[D&D] Deities & Demigods cyclopedia; James M. Ward, and Robert J. Kuntz; 1980
[Dr.65] Dragon Magazine #65; ?Tuatha De Danaan: A revised Celtic mythos;? Robin Emrys Atkinson; September 1982
[Guide] A guide to the World of Greyhawk; Gary Gygax; 1983
[T1-4] The Temple of Elemental Evil; Gary Gygax with Frank Mentzer; August 1985
[L&L] Legends & Lore; James M. Ward, and Troy Denning; 1990
[Aerth] Epic of Aerth; Gary Gygax; 1992
[OJ12] ?Thus Spake Gary Gygax: Ye Secrets of Oerth Revealed;? Paul Stormberg; Spring 2001
[Celtic] Celtic Age: Roleplaying the Myths, Heroes and Monsters of the Celts; M. Bennighof, Ph.D., J.R. Phythyon, Jr., and R. Soesbee; 2002