This item is fished from the fountain in Dalaran.
Antonidas was an archmage and the leader of the Kirin Tor and Dalaran. He served the Alliance in both the Second and Third Wars. During the Third War, he was killed by Arthas who was trying to get the Book of Medivh.
The quote on the coin is a rephrasing of the Serenity Prayer: "Grant to us the serenity of mind to accept that which cannot be changed; the courage to change that which can be changed, and the wisdom to know the one from the other."
The quote on the coin is similar to the blood elf joke: "Give me the serenity to accept the things I cannot change, courage to change the things I can and the wisdom to... *angry grunt* Just give me some freakin' magic before I kill somebody!"
- Patch 3.0.2 (2008-10-14): Added.