As said above you select character perks in your legacy panel and there you can unlock him, there will be 2 boxes, one is for unlocking him on a republic character and the other for a imperial character.
You need to be on the character you want to unlock him on and it will cost 1 million credits OR 350 cartel coins.
Sadly there isn't a option to unlock him on all character, you have to unlock him on each one paying full price on each character.
Statement: That's what I thought.
Agreement: Sadly indeed.