Assistants in ESO are like pets but they perform a function too. They are arriving with Update 9 (Thieves Guild, March 2016) and the first one will be as a reward for completing the Thieves Guild DLC quest line.
You can activate Assistants like pets, they will follow you around and you can talk to them. You can only have either an Assistant or a pet active at the same time. They’ll work throughout Tamriel except for Cyrodiil.
Pirharri The Smuggler
This Baandari Pedlar is on hand whenever she is needed (except in Cyrodiil), and will fence any of your stolen goods for you – but she’ll take a cut of your profits.
You can call her up on the Assistants tab in the Collections UI. She is required after completing the Thieves Guild quest line.
Tythis Andromo The Banker
You can buy a banker NPC Assistant called Tythis Andromo the Banker on the Crown Store. This Assistant will be able to bank your items for you while out and about.
Nuzhimeh the Merchant Vendor
You can buy a vendor merchant NPC called Nuzhimeh the Merchant on the Crown Store. This Assistant will let you sell things to her and will be able to repair your gear.