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