Firstly, see the Gaiapedia article Angelic Halo.
The Angelic Halo is Gaia Online's first Monthly Collectible item from June 2003, at that time it was referred to as Donation Item due to the fact that the members of 2003 donated to Gaia out love for the site and to give encouragement to the Administrators. Many donated without the expectation of not receiving anything in return, but members were surprised to find a sealed envelope in their inventory and within that envelop a gold Halo.
Since its creation Halos have been just one of the most popular items when it came to spin-offs and imitations. The Mythrill Halo is the 100th Monthly item and was modeled after the Halo. While the Dark Halo is a considered counterpart to the Angelic Halo.