(Note some of the Lore may not be in order, or the years between stuff isn't right, i done this off the top off my head..)
Slashbash Moorback was born and raised on the human settlement of Andorhal, the grain distributing capital of Lordaeron, his father worked at the local mills, providing the kingdom with food, when the Third War broke out, Slashbash was at the tender young age of fifteen, but he was still under the legal age to fight, but he really wante to kill any Undead scum that ever tried to disrupt the peace of his homeland.
After Andorhal's inhabitants were turned to undeath by the plague, the plague was spreading fast and had ravaged most of northern Lordaeron,but grain was still being distributed, as they had found out shorly before killing Kel'thuzad, Slashbash, now 16, went with his Prince, Arthas Menethil and Jaina Proudmoore to check out the ruined city of Stratholme. where they would meet Uther Lightbringer, (who would be stripped of command), and after a bit of arguing, Arthas went inside Stratholme to begin the Culling. After the Defeat of Mal'Ganis, Arthas and Slashbash headed to Northrend to end it. As Slashbashs' 17th Birthday encroached, Arthas went looking for Frostmourne, Slashbash was left behind with soldiers such as Luc Valonforth to Defend thier campsite from Mal'Ganis's endless waves of Undead. But when the Prince returned, hope filled the warriors heart, as they "slew" Mal'Ganis...
However, a the days went by, Arthas was corrupted by the blade and when the troops were ordered to go back to Lodaeron by Uther Arthas ordered the ships to be burned.
This would be his Undoing, as months later the Prince would return to Lordaeron, as a Death Knight. Slashbash however didn't return with the prince, he migrated to Theramore, assisted in the kiling of Daelin Proudmoore, and helping Jaina build up, a city for the survivors of Lordaeron. And when that dreadful day came, Slashbash heard the call to arms, as the leaders of the mortal races met at Hyjal Summit, called by Medivh, they fought for blood and honor in The Battle For Mount Hyjal, which ended the third war.
Slashbash has since then become one of the greeatest warriors, to ever live.
Slashbash joined the Argent Dawn, untill the defeat of Kel'thuzad when he ventured to Outland to help in the fight against Illidan, after Illidan was slain, there was trouble, in Quel'thalas where the Amani tribe had rebooted, and thier leader Zul'jin had formed Zul'Aman into a fortress, but the brave heroes still triumphed and defeated the Amani Empire, right on their doorstep.
Slashbash participated in the Battle at Light's Hope in the plaguelands, weeks before the Expedition to Northrend, and he was one of the many survivors, that lived to see Northrend crumble, and eventually, the Argent Crusade assault Icecrown Citadel.. this is where he is currently located, atleast, we think..
Will he ever get out of Icecrown Citadel, I don't know we'll have to find out in patch 3.3.5