I DM a Savage Worlds game with six players. I'm coming on this problem where some of the characters tend to bully one of the other characters.
For context, the character getting picked on is played by "Bob." Bob's character is young, naive, silly, and his homebrewed power is unpredictable, he summons monsters based on a d20 roll.
Bob is able to get into character much better than any of the other players, taking on a voice and distinct personality. However, his character is somewhat annoying. He tends to mispronounce people's names, he always walks up to random NPCs and asks to be friends, and he can sometimes gets sassy with people. Of all six characters, he's my favorite because he plays his character so well. This character is also one of the most developed, he's gone through some serious trauma and he copes by making, and keeping friends. He doesn't want to lose anyone.
The others have all decided to be edgy, unfriendly characters. They tend to gang up on Bob's character, deliberately trying to cut him out of the story, going off and leaving him places, grabbing his things (sometimes physical items I made for Bob's character) and refusing to give them back, interrupting and talking over him. At one point I had to create an NPC to guide Bob's character back into the story because everyone else ditched him.
I could understand this better if Bob's character was useless, but he's not. He's intelligent, he's powerful, and he's generally friendly, and I feel he drives the story more than everyone else. Everyone else seems happy to spend the session buying armor and comparing prices.
How do I get them to work more like a team and stop picking on one character?
Bob is frustrated because he's created a deep character with a motivation, a backstory, and a personality to match, but he keeps getting left out. It really bugs me because honestly, Bob's character is my favorite. Any advice on how to deal with this?