Here is the full list of all 39 Vikings - there are Wolves of Midgard achievements.
Complete all Trials.
Complete the game as the Warrior.
Complete Campaign 3.
Unlock level 4 of the Shipmaster.
Unlock level 5 of the Smithy.
Become chieftain of all the clans.
Complete Campaign 2.
Burn the Imperial Fleet.
Rage continuously for over 20 seconds.
Earn 1,000,000 Blood.
Kill 100 Jotun.
Unlock all Gifts in Skathi's gift tree.
Liberate Flotnar village.
Complete Campaign 1.
Keep Draupnir for yourself.
Travel to Utgard.
Survive the Mire-Witch's spell.
Kill four foes in a single attack.
Equip three runes on a single item.
Killed 500 Tomte.
Perform 1000 rolls.
Complete any Hunt map.
Defeat the Jokul.
Defend Ulfung Village.
Complete the Imp Hunt.
Complete the game as the Shieldmaiden.
Complete Game+.
Complete the game on the highest difficulty.
Unlock all Gifts in Loki's gift tree.
Unlock all Gifts in Odin's gift tree.
Unlock all Gifts in Tyr's gift tree.
Unlock all Gifts in Thor's gift tree.
All Hunt maps complete.
Found all Legendary Items.
Earn 50,000 gold by selling resources.
Complete all Challenges on all maps.
Collect one of every rune.
Accomplish campaign in Valhalla Mode
Accomplish campaign in Valhalla Mode on highest difficulty.