Bisarane is the leader of the House of Sorrows. You meet him for the first time just past Foe's Hearth, west of the Proving Halls, where he asks you for help. He gives you the quest, The Sorrows Call, which is the first quest of the House of Sorrows faction.
He doesn't care why you join his House, as long as you can help him.
Many in the house of Sorrows don't see Bisarane as their true King. He was appointed the King of Sorrows when the House made a pact with the Tuatha : They would leave the House alone, but in return the House would not be allowed to intervene with the war. In addition, the House would get a new King which would uphold the pact - thus Bisarane became their King. However, the House refuses to listen to him any longer once Saturnyn leads the Tuatha on an open attack against the House and many lose their faith in him completely once he invites the Fateless One to join the House, many believed he crossed the line and made his final error by letting a mortal join their ranks.
NOTE : Many have a hard time finding Bisarane. He is located on either path going out of Cursewood; whichever one you took first.
If you go through Shattertier Mine and out of Foes' Hearth (thereby bypassing the path out of Cursewood), Bisarane will not appear until you actually use the path. Running from Foes' Hearth back into Cursewood is the easiest way to make him appear.