Revenge ideas in Lankhmar

So I am designing a custom thief-centric campaign in Lankhmar.
This is placed before the Twain have gained any fame.

I need my main PC to be instilled with revenge, enough to fuel one of the long term story threads.
I also am increasing the Lovecraft influences to be more prominent in the background, so a cult of some sort will be one of the many main adversaries.

Since I have gotten great feedback on my other questions, feel free to throw ideas at me or let me know what revenge motivations you have placed on your players in the past.
Thanks!

I don't place motivations on my PCs, rather I work with the PCs to help develop their own ideas. Not all players enjoy backstory, some prefer the story that happens at the table with the party to be what drives them. So my advice is that you have three ways to work it into your campaign, and I've used all three successfully. Plus they aren't mutually exclusive.

1. premade characters people can choose from and build the revenge hook into at least one of them. Alternatively, premade campaign hooks people can choose from and one is the revenge hook. The advantage here is the player buys into it. The downside is more work for you. See an example of it here.

2. hold a session zero and explain that you want a revenge story. You want at least one person to be driven by the motive of revenge but offer to help link other players' backstories to that one as the way the party came together so it can be a shared motive for two or more. Do NOT try to force it on anyone. The idea here is to recruit a willing partner among the PCs.

3. If people say they prefer to have the backstory minimal and really focus on what happens in game, then work it into the first session with PC permission. You don't have to go so far as to kill a PC in the first session, but that can work (if you really know your players well, do not try it with strangers). But put the event that is to drive the revenge into the session. Start in the middle of the action. I have even seen a session start with the players controlling NPCs. Each one selected one person from their own backstory and chose an NPC stat block for the person. The campaign started with the PCs controlling those NPCs in the past. The NPCs had the experience (BBEG curses the kingdom) and scatter. Years later people they met and told the story to come to the cursed kingdom to save it. Hard to run without being a railroad, like if you kill a critical NPC you need to trust the player will be ok with re-writing their backstory (oh my dad just died before I was born? Lol, ok how about if that was my uncle not my dad it happened to and when his brother died it motivated him to...).

And again these can all be combined.

Also there are some classes that work really well with the idea because the class mechanics can be loaded with story. Vengeance Paladin is the obvious one, but don't overlook a warlock who took the power for the sake of revenge. Or the assassin who is training to kill someone specific. Or the ranger whose favored enemy was selected because of a specific person or entity or creature.

Thanks for the feedback, always good to hear how others approach things.