Razalaxx was a member of the Revenant Vow, a mercenary company set in Tor. Another member of the group - Bhaltair - received letters from his sister about how her village Orlane was in danger, and so the group went to investigate.
With Orlane saved from the spirit naga Explictica Defilus, Razalaxx was recognised by the blacksmith's daughter, Keyleth, who has pledged herself into his service as his squire.
The Battle at Castle Greywall
The Revenant Vow, now heroes of the village, search for the disappearance of The Righteous Squad of Questing Adventurers, another band of adventurers and allies of the Revenant Vow.
They soon learn that the Scion of Orcus have captured the group and was using them in a ritual to summon Orcus (though he wasn't powerful enough to perform such a rite). During the final battle, members from both groups have perished, but the Revenant Vow were victorious. The Scion of Orcus was killed, but Lady Sariel is now a threat.
After the battle, The Righteous Squad of Questing Adventurers went their separate ways. While the remaining members of the Revenant Vow went to Tor Keep to search for a way to save Lady Sariel, Razalaxx and Keyleth returned back to Orlane to help the civilians out and later excavate the ruins of Castle Greywall.
As Above, So Below
After hearing a commotion at the inn, Razalaxx went to investigate and met up with Vorrikus, a former Mul fighter for Ajax, and Edric, a priest from Orlane. Unlike the civilians, Razalaxx was welcoming towards the two and made everyone within the inn feel bad for the way they treated Vorrikus and especially Edric.
A few days later, Vorrikus and Edric joined in the excavation at Castle Greywall, the day they discover the Mirror of Gilmarra, a magical artefact Lady Sariel desired. The following night they were assaulted by ghouls created by the vampire queen to steal the mirror, but Vorrikus and Edric were able to fight off the creatures. Shortly after Razalaxx arrived the next day, Duergar appeared out of a hidden door and a great battle was fought, but Razalaxx, Edric and the mirror was taken below.
The World Below
Razalaxx was later found dead by the Revenant Vow and The Shield of Gravesford from the Mind Flayers, but was later resurrected from the gnomish queen of Xanxarite. Having a vision from his deity, Razalaxx saw Tor burning and a "beast with many heads". With their friend saved, the Revenant Vow leave the World Below and return to Tor.
At some point before The Siege of Castle Rend, Lady Sariel fought the Revenant Vow, and Razalaxx's fate is left uncertain.
Behind the Scenes
Sir Razalaxx was Silvano's player character in the Revenant Vow campaign. After the adventure was over, Matt Colville made him an NPC in the Shield of Gravesford campaign.