He previously worked for Maven Black-Briar, but, during a job transporting the Quill of Gemination across Lake Honrich, he crashed the boat and lost the quill. Since then, he's been in debt to Maven and worked as a guard watching over Riftweald Manor, owned by Mercer Frey.
Vald also used to have a close relationship with Vex.
During the quest the Dragonborn must infiltrate Mercer Frey's house; however, Vald is keeping guard of it. In doing so, Vald will become hostile and must be killed to gain entry.
However, if the Dragonborn speaks to Vex, she reveals that Vald only cares about money and that erasing his debts with Maven Black-Briar would gain his good side. If the Dragonborn speaks to Maven Black-Briar and asks to have his debt erased, then she will ask the Dragonborn to find the lost Quill of Gemination, which is locked in a strongbox in the wreckage of Vald's ship in Lake Honrich. If Vald cannot be spoken to because he is attacking, spells like Calm or Harmony to make him stop. For those that have not trained their Illusion skills to a high enough level yet when those don't work, but happen to have the Bend Will dragonshout from the Dragonborn DLC, can also use this shout to calm Vald so that he can be spoken to.
Upon retrieving the quill and returning it to Maven, she will erase Vald's debt. Informing Vald that his debt is erased will result in him happily allowing the Dragonborn into Mercer's house before leaving Riften.
A way around this is to lower the ramp, as this should make him unlock the door and attack. Let him attack and then kill him, or have NPCs kill him. Either way works. Now it is clear to proceed with the quest.
- If you try to pickpocket the key from Vald and are detected, you will not be able to talk to him after giving Maven the Quill. Even paying off any accrued bounty will not make it possible to talk to him. Dual casting an Illusion spell (such as Calm) with the relevant perks may be the only way to make this possible.
- Sometimes if you try to talk to Vald through the fence after collecting the quill for Maven and getting his debt cleared he will turn hostile and run around looking for you. Go around to the other fence behind the building (past the theives guild entrance) and he will walk up to you and initate conversation.