I have a player that is struggling to come up with his backstory and consequently for me, a hook to pull him in. His character is a human fighter, taking on the role as a bounty hunter. My other 4 players have decent backstories that have allowed me to pull their characters into the plot(s). At this point, I am thinking that for my human fighter I could have a prison break and some of those who he caught have returned to their "gang" and these gangs are now after the character. Something like the mafia is going after the one player and he will need to bring the whole organization down to be free of them.

Thoughts?

BBEG ideas for the encounters? Just thugs and bandits?

XGtE has a section on building character backgrounds that you can use as a starting point. If you have access to that, you two can use it as a starting point to come up with some backstory elements. You don't have to use everything you roll, it helps to know 'no, I definitely don't like the idea of X being a backstory element' just as much. But it can give you two something to start from.

I think there is a lot of cool ideas for a bounty hunter:

• Maybe the organization that hired him has now turned against him. Sending their best after him. Who hired them and why did they so easily turn on him?
• Maybe he is sent to find one of the PCs and lock them up but realizes that they are not at fault or change their mind about them. Might lead to great PC moments
• They might be sick of their life as a bounty hunter but nobody just stops being a bounty hunter.
• They might have been taken a contract that turned out to be an assassination and they didn't go through with it.
• Maybe they are infiltrating the bounty hunting organization to learn who the leader is because they were responsible for taking away a loved one?

Maybe he's been hired to hunt a Moriarty kind of criminal. A nebulous grey entity, that's the mastermind behind kingdom-spanning crimes. You can throw tiny bits of his involvement to your player(s), maybe he's involved with your "real" BBEG, or more likely takes advantage of the things your BBEG causes to happen. Though, this would heavily depend on your general setting and is less suitable for prewritten modules, or very streamlined plots.

Hello, 

I love the way how you can create and build relationships for a character via using the Resource "XANATHAR'S GUIDE TO EVERYTHING"! Chapter 1- Character Options - This Is Your Life (Last part of the resources chapter!)

It has an awesome way (using dices) to determine your character's backstory (Origins, Personal Decisions, Life events). I use it as a first thing with every player individually to help them shape the character. 

It contains several tables that help you navigate what happened in childhood, what life events you have had etc. This can spark ideas and further development of the character's personality. It takes approximately 1 hour for an okay background or 1,5 for more elaborate.

I usually take notes and copy and paste those decisions to ChatGPT and summarize them (the notes) amazingly in an easy and digestible way for the player to revisit. 

Secondly, I always ask for a character flaw (suitable for the campaign, -the example I had a marsh/swamp environment and one of my players was unlucky and kept sneezing because he is allergic to mold spores - this resulted in a few broken stealth missions, funnier combat etc!). You can (once again) as ChatGPT "For DnD character create a d20 roll for their flaw/quirky behaviour with a set of rules and consequences). 

Here is a list of tables you can roll for (without details of course) to give you an idea of what material is in so you can decide if it is worth investing in.
Origins:
Parents - dead or alive, half race+half race? , 
Birthplace and order of when you were born
Siblings, how many, current status (dead or alive, relationship with them, occupation etc)

Example: One of the guys was seduced by a silver dragon :D - Silver dragons apparently love human dining and food and he was a really awesome cook!  (That was a lot of fun!) and now he is on a personal campaign to create a party (almost an army) of thugs, soldiers etc who will help him free the dragoness (who was accused of kidnapping children and was taken into prison) (All info is based from here - https://forgottenrealms.fandom.com/wiki/Silver_dragon ) 

For encounters I do recommend different settings and not so much used monsters (like Stirges :D they can wreak such havoc!)
Childhood memories (and more)

Personal decisions
Here you can role for race, class, background (plus why)
Life events (how many + what happened) with supplementing tables like boons, adventures, illnesses etc (weird things are my fave!!!)

And many more I will not list :) I do recommend this resource and having a pre-session with every player separately. This way you can help tailor it for your campaign style and create engagement and relationship with the characters. It can also result in some cool ideas for pets, sidekicks or different weapons, shapeshifts, items etc.

Quote from PeachkaSlayer >>

I have a player that is struggling to come up with his backstory and consequently for me, a hook to pull him in. His character is a human fighter, taking on the role as a bounty hunter. My other 4 players have decent backstories that have allowed me to pull their characters into the plot(s). At this point, I am thinking that for my human fighter I could have a prison break and some of those who he caught have returned to their "gang" and these gangs are now after the character. Something like the mafia is going after the one player and he will need to bring the whole organization down to be free of them.

Thoughts?

BBEG ideas for the encounters? Just thugs and bandits?

I would want to know why the character originally became a bounty hunter, and why they left that job to become an adventurer

If you have answers to those questions, you should have a better idea of the kind of story hooks that will catch their interest