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