Okay, this is starting to get freaky.
In Riften, I met a guy named Louis Letrush. A rich Breton, he complained to me that he bought an expensive horse from Sibbi Black-Briar right before the latter got jailed for murder. He still wanted his horse delivered, though, but the Black-Briar family refused to acknowledge the deal had even taken place. I took it upon myself to deliver the horse to him, which I eventually did. He rode off into the sunset on his brand new horse.
A bit later, near Markarth, I was exploring when I came upon Louis Letrush once more. This time, he was on foot, and being chased by an Orc mercenary. I rushed forward to intercept them, but before I got there the Orc cornered him. He told Letrush "Maven Black-Briar says hi", and shamelessly cut him down. I finished off the Orc, but Letrush was dead as dead can be.
A bit later, I take the carriage from Markarth to Whiterun. I arrive outside the city, and notice something odd... There's a person sticking through the ground right in front of the stables. It's Letrush, and he's alive. He doesn't move, he doesn't have any dialog options, he's just submerged partly into the ground, with an animation like he's still sitting on his old horse. I tried my best to ignore him, and carried on.
Now, however, shit got extra freaky. I was travelling home from Windhelm when I arrived at Whiterun. I notice there's an NPC standing besides Letrush... A very familiar NPC. It's another Louis Letrush.
Pardon the shitty picture.