Prisoner 237 / Gandareth escaped Revel's End with the events of Horrifying Halls. He was designated "Fugitive Beta" in the official report by the Harpers investigator Estilël Farwind.
He had served 53 years of a life sentence. His story to fellow prisoners was:
I was a city official in Baldur's Gate. I embezzled city funds to pay for my dear wife to be resurrected.
The actual crime was 19 counts of first degree murder in Baldur's Gate. He was deadly follower of Bhaal, the God of Murder. Though he seemed to kill as a form of worship, his reputation brought him into close ties with notorious members of The Guild. Gandareth has occasionally cooperated when information on that criminal organization has been needed - just enough to be kept alive (and imprisoned far from their reach). He was also considered a heretic by the Church of Cyric, for not recognizing Cyric's claim to Bhaal's domain (Cyric had gained divinity through killing Bhaal in 1358 DR) - and negotiated his imprisonment for protection from agents of Cyric (in particular members of the Zhentarim).
Reward from the Lords Alliance: 1000gp live, 20gp information leading to capture, 100gp for proof of permanent death
While serving his time at Revel's End, Patricia Ioria, a fellow prisoner, converted Gandareth's fanaticism to worship Tiamat. Bhaal's mark on the world had continued to fade to Cyric, and he found the raw power for destruction in the Queen of Dragons appealing. Despite being captive, Patricia communicated with the crafty Inconnu Arauthator ("Old White Death") through spirits the dragon was able to sneak in and out of the prison. Though Patricia's life sentence ended with her dying of old age, the visits from the dragon's spirits continued, shifting to Gandareth. In recent years, the plotting of Severin Silrajin to subvert the Cult of the Dragon appealed to both Arauthator and Gandareth.
In the prison break of Ches 25th in the Year of Three Ships Sailing, Gandareth was able to evade the oblex and escape to the tundra, where Arauthator picked him up and brought him to a contact in Fireshear, where he sailed by ship to meet with Severin (and became a Purple Robe). Earning his place through tremendous ruthlessness, the failures and eventual death of Varram have led to Severin naming Gandareth the new White Wyrmspeaker and dispatching him on missions in the north.