Ransin Donner is a level 35 small pet keeper located in the Forlorn Cavern in the dwarven city of Ironforge.
People who attended BlizzCon 2005 and received a card with a code on it can give their code to Ransin for the blue Baby Murloc, Murky.
People who attended BlizzCon 2007 and received a card with a code on it can give their code to Ransin for the Murloc Suit.
People who attended BlizzCon 2008 and received a card with a code on it can give their code to Ransin for the Big Blizzard Bear.
In dialog, he offers both choices, so both are still current and available. Presumably if you choose the wrong one, the code for the other one won't work.
A sample Murky, the blue baby murloc small pet, is standing by him. (June 6, 2008) It appears to lack the periodic song and dance animation.
Ransin Donner is the Alliance NPC for redeeming the code for Gurky, the pink baby murloc, but in dialog he no longer offers that option (June 6, 2008).
From Blizzcon 2007 through sometime in the first half of 2008, Ransin Donner wore the Murloc Costume.
Ransin had a companion, Garel Redrock who could accept the code for the Baby Murloc, but Garel Redrock is currently no longer present. (June 6, 2008)
Zas'Tysh is his Horde counterpart.
See List of Ironforge NPCs.