I second Bloody Initiate on that stuff about the "one who re-occurs because they actually made it.".
As a GM i once threw a necromancer at the party (in the old AD&D days) as a final boss to a low-level adventure. The guy threw everything he had at the PCs, to the point he even started throwing furniture as he ran out the door. He eventually escaped the PCs through a series of secret entrances with a single HP! As the PCs searched and eventually found the escape route, a magic mouth shouted a "thank you for the entertainment" and "see you soon" message to the party...
Another thing that actually worked (at least for me as a PC) was seeing the same guy over and over again, but always as a secondary man. English isn't my home language, so i'll try to explain it as best as i can...
In a series of home-brewed adventures, we (the party) were always tasked to search something or hunt someone to bring him to justice (or just "deal" with him). As we strolled to complete the mission, we kept seeing the same NPC, over and over again. In this case it was a sort of fighter, maybe a ranger, wielding two swords and wearing a trademark ivory-colored armor and blue cloak. He kept passing us on the roads riding in the opposite direction, apparently escorting a some noble or speaking to a sargent of the enemy army and riding in haste before we even got there; riding with his gang on a distant hill...
We never got to know who he was, what was his role, if any, in the grand scheme of events, but the "misterious stranger" theme appealed to our party. The simple fact of him being "just beyond reach", made us eager to catch him, question him or whatever...
This isn't exactly a hate thing, but it undoubtly turns the NPC towards "alert mode" or "curious mode" instead of "indiferent" or "let's-just-kill-him mode"...