Sigurd makes no secret on his appearance and looks a stereotypical thief.
Sigurd is a third-level Rogue, with the Arcane Trickster as his Roguish Archetype, and a third-level Monk, with the Way of Shadows as his Monastic Tradition. He also wields a sun blade.
Against the Cult of the Reptile God
Sigurd, alongside the rest of the adventuring party, joined Bhaltair in his trip to Orlane to find out what has happened to his missing sister. They learn that the village is under the domination of the spirit naga Explictica Defilus, and later meet up with the ghost of the mayor of Orlane. The group swears fealty to this revenant, hence becoming the Revenant Vow.
Keep on the Shadowfell
After Orlane was saved, Sigurd then decided to try and find out what has happened to his brother, Andavari, and the rest of the Righteous Squad of Questing Adventurers. This leads him to resort to horrific methods of receiving information, such as burying a prisoner up to their neck or cutting off another prisoner's finger.
The Revenant Vow eventually learn that Kalarel the Vile has captured the Righteous Squad of Questing Adventurers at the Black Keep as an attempt to summon Orcus. After a battle against a group of slaadi, they discover that Gynk the half-orc ranger was trapped in the slaad nest, Sigurd quickly recognizes him and frees the half-orc.
With Gynk leading the Revenant Vow, they all arrive at the ritual room. They see Kalerel, many of his minions, and the Righteous Squad of Questing Adventurers, including Gynk. Lady Sariel then realizes that the Gynk they were with was the green slaad that disappeared from their previous battle, and Gynk attacks Sigurd.
Despite losing Lady Sariel and Ellasym in the battle, in addition to some of the members of Righteous Squad of Questing Adventurers, the Revenant Vow proved victorious against the battle, and successfully escape the collapsing keep.
As Above, So Below
During his downtime at Tor Keep, Sigurd says farewell to Andavari and begins to set up his thieves' guild, later receiving a letter from Cora talking about recruits. Sigurd also begins to search for a wizard that is capable of restoring a cursed soul, to save the now vampiric Lady Sariel, coming to the conclusion to finding the wizard of Bedegar, Tace.
However, the mul Vorrikus arrives at Tor Keep to alert the Revenant Vow that Sir Razalaxx has been taken to the World Below. Although Keyleth decides it's best to stay at Orlane, Sigurd (alongside Hnossa and Bhaltair) joins Vorrikus in heading into the World Below to recuse Razalaxx.
Behind the Scenes
When creating his character, Lars decided that Sigurd and Andavari (his previous character) were brothers and that Sigurd was searching for his missing brother. Because Sigurd was willing to do whatever it took to find his brother - regardless of how ethical his actions were - Matt changed Sigurd's alignment to evil.