Galakrond
Murozond
Chromatus
Revived Deathwing
Unknown evil dragon
Xal'atath
Revived Y'Shaarj
Unknown Old God
Corrupted Titan-forged
Azshara
Zovaal
Fact (because I say so): TBC > Cata > Legion > ShaLa > MoP > DF > BfA > WoD = WotLK
My pet collection --> http://www.warcraftpets.com/collection/FuxieDK/
Didn't it say somewhere that Galakrond's remains were removed from the Dragonblight (for a revive)? Pretty sure it was a datamine.
Technically, the boss was named "Wrathion: The Black Emperor," which is not a title Wrathion ever claimed, and his appearance was more akin to Deathwing's in Cata, which Wrathion doesn't have in his dragon form. All in all, both in lore and fundamentally, the first boss of Ny'alotha wasn't Wrathion at all, just a projection of Wrathion's possible corrupted state.
"We're more of the love, blood, and rhetoric school. Well, we can do you blood and love without the rhetoric, and we can do you blood and rhetoric without the love, and we can do you all three concurrent or consecutive. But we can't give you love and rhetoric without the blood. Blood is compulsory. They're all blood, you see." ― Tom Stoppard, Rosencrantz and Guildenstern are Dead