Baldr Armstrong, also called Baldr the Strong Arm, is a Viking boy of the Stormchasers tribe and son of their clan's Chief. Baldr is a natural warrior with fierce determination and strength and was the original trainer of Stormfront, though Baldr had chosen a terrible name for the Skrill before it was renamed by Sigrid Henderson. Sigrid, in fact, was also Baldr's betrothed, a marriage organized by their fathers, very much against Sigrid's will. Despite her protests, Baldr is determined to have her as his wife, not out of affection or romantic love, but rather out of a love of the notion of having a wife to do everything he wants. Stormfront eventually abandoned Baldr in order to leave Stormchaser island with Sigrid, whom he struck a bond with. Angered at Sigrid for "stealing" his dragon, Baldr leads a small troop of his fellow warriors to retake Stormfront and bring Sigrid back to Stormchaser island to face justice for her actions as well as becoming his wife once and for all. During this time, Baldr temporarily took over as the rider of a Monstrous Nightmare named Brute.
He briefly caught up to Sigrid while she was on Berk, but lost her when he was distracted by Dagur the Deranged, who also wanted Stormfront.
- Baldr is named after the Norse god of the same name.