The identity of the "Nuckelavee" haunting Lallybroch in Outlander has finally been revealed in Season 7, Episode 6. It was discovered that the intruder was Roger's ancestor, William Buccleigh Mackenzie, who had time-traveled from the 18th century. Roger reacts violently to Buck's presence due to their tumultuous history. Buck was initially portrayed by Graham McTavish in Season 5, but was recast with Diarmaid Murtagh for Season 7. The recasting may be related to the upcoming storyline involving Roger, Buck, and a younger version of Dougal Mackenzie.