I think I figured it out.
The dude on the left is the only person that John Teller trusted to work on his bike.
Potter is his son, and he wants to take down SAMCRO because he holds them responsible for his father's death.
He wants to take the Irish down, because he thinks his father would still be alive if it wasn't for the gun-relationship between the IRA and SAMCRO.
Remember, Clay wanted JT dead because he was going to push for the club to get out of the gun business.
According to Gemma, Clay must've convinced Potter's dad to mess with JT's bike, and then Clay had Potter's dad killed a week later to cover his tracks.
So Potter grows up thinking his Dad died because Samcro wanted to keep supplying guns to the Irish.
He becomes a Federal prosecutor and makes it his life's mission to take down SAMCRO and the IRA for killing his father.