|This article or section is likely to dramatically change once Legion begins.
Thassarian is the first death knight to join the Alliance. As a young man, he joined the Lordaeron army hoping to follow in his father's footsteps. Thassarian followed Prince Arthas on his expedition to Northrend, where he was slain and reanimated by the Scourge. He was forced to kill his own mother to prove his loyalty and took part in the scourging of Lordaeron and Quel'Thalas. One of the few death knights of Acherus who maintained a genuine sense of honor and brotherhood, Thassarian developed a strong bond with the elf Koltira Deathweaver despite being enemies in life, considering themselves brothers in death.
During the Battle for Light's Hope Chapel, he was freed from the Lich King's control along with many other death knights and joined the newly-formed Knights of the Ebon Blade under Highlord Darion Mograine. Thassarian then traveled to Stormwind to serve King Varian and became the first death knight to rejoin the Alliance. He reunited with his sister Leryssa while fighting in the War against the Lich King. After the war, Thassarian remained a loyal soldier to his king while also maintaining his friendship with Koltira, even when they were forced to confront each other during the Battle for Andorhal.
Thassarian was a soldier of Lordaeron during the Third War. He traveled with to Northrend to hunt . When Arthas and went missing, he went to search for them alone. He discovered Frostmourne Cavern, where he found Falric. Falric, already converted to a Death Knight by Arthas, slew Thassarian, and thus began his unlife as a death knight.
Thassarian returned to Lordaeron with Arthas and assisted in the massacre of its citizens. Arthas forced him to slay his mother, , to prove his loyalty. This horrific event continued to haunt him, and it remained perhaps his last scrap of humanity for some time.
Arthas' assault on Quel'thalas introduced Thassarian to the high elves and his brother, , at An'owyn, where he pursued the mooncrystal to open the second moongate and proceed with their attack. Thassarian nearly killed Faltora, but, upon remembering his mother, he decided to show a moment of mercy. He returned to Arthas with the mooncrystal that he recovered. Koltira later confronted Thassarian and questioned why he didn't murder his brother, hoping to convince him to regain his humanity. This attempt failed, and Thassarian killed Koltira, who was returned to unlife as another death knight. Koltira and Thassarian developed a significant friendship that lasts to this day.
Years later, the ordered his death knights under the leadership of to attack Light's Hope Chapel using the necropolis Acherus with the goal of raising the thousand or so Alliance soldiers buried beneath it to bolster the ranks of the Scourge. The attack on Light's Hope Chapel ended with a defeat for the Death Knights. Many of the family of the Death Knights were buried at Light's Hope Chapel, and the spirits of their relatives rose to convince them to lay down their weapons. Thassarian was convinced by his father, , to stand down. Mograine declared the independence of the Knights of the Ebon Blade. Thassarian traveled to Stormwind and met with who accepted the Knights of Ebon Blade as allies and readmitted its members as members of the Alliance.
World of Warcraft
In Wrath of the Lich KingThis section concerns content exclusive to Wrath of the Lich King.
He is first encountered in Acherus: The Ebon Hold as a level 55 standing next to and . In phase two after completing  , he relocates to the Scarlet Tavern with Bloodbane, where he is involved in the following quests:
He shows up at the Battle for Light's Hope Chapel as a level 60 elite taking part in  .
Thassarian can later be found aboard the Alliance airship the Skybreaker above the skies of Icecrown. He is involved in quests that unfold The Shadow Vault among others. He also plays a part in the unfolding storyline of Wrath of The Lich King.
In CataclysmThis section concerns content exclusive to Cataclysm.
The Alliance and Forsaken are fighting over control of Andorhal and the remaining Scourge presence there. The Alliance, led by Thassarian, have taken control of the western portion of the town while the Forsaken, led by Koltira Deathweaver, have taken control of the eastern portion. Over the course of the Battle for Andorhal Thassarian sends Alliance heroes to deal with the remaining scourge forces and after defeating the leaders, Thassarian and Koltira enter a truce. Some time afterwards Alliance forces launched a failed assault on the Forsaken. During the Forsaken counter attack Thassarian flees and his minion Lurid is killed. 
In LegionThis section concerns content exclusive to Legion.
Thassarian returns in Legion as the Death knight player's first Champion, and he sets you on the course to return the four horsemen to serve you.
MangaThis section concerns content exclusive to Warcraft-related manga (or manhwa).
- "All I ever wished was to serve once again. For humanity, against a .
- Instead, I find that our numbers have been infiltrated by cultist scum.... and all of the signs point to Naxxanar as the origin of this rot."
- "With the death of the The Lich King, all I have left is my duty. There is no family, there are no friends... there is only this. War."
- Even while he was in service of the Lich King, Thassarian seemed to be a noble person. After sending the player to rescue Koltira Deathweaver — against the code of the Scourge death knight — asked why he cared. Thassarian replied that, though they may have been hated enemies in life, "In death, we are brothers."
- His blades use the same model as the two-handed sword .
- ^ a b c d e f Death Knight (manga)
- ^ Cataclysm Lore Details - World of Raids Forums
- ^ http://www.youtube.com/watch?v=Fsw78wHlhrE&feature=channel
- ^ http://forums.worldofwarcraft.com/thread.html?topicId=25968750004&postId=262602230514&sid=2000#39
- ^ http://www.blizzplanet.com/blog/comments/warcraft_death_knight_front_cover
|Ebon Hold||Scarlet Tavern||Light's Hope||Wailing Ziggurat||The Skybreaker||Andorhal|