Xunlai Agent

These are special NPCs that oversee a network of "magical" storage vaults. For the one-time fee of 50 gold, a player can create a "storage account" with the Xunlai, allowing that character to access 20 additional inventory slots in any outpost, city or mission location in the game after the Searing. In addition to the expanded inventory, Xunlai Storage allows a character to store up to 1000 platinum in storage, as opposed to the 100 platinum limit on their personal inventory.

Note: All of the characters of a player's game account will share the same storage account (allowing a player to pass equipment and/or gold to his other characters), but each character has to pay the one-time fee.

Because Guild Wars has such limited inventory space, and such a variety of crafting material and items, purchasing a storage account with the Xunlai is widely considered essential.

History
The Xunlai Agents are members of the Xunlai Guild - a long-trusted agency. They give you some backstory about the Xunlai Guild when they ask you if you wish to pay the 50g fee and open a storage account. The Xunlai Agents have the appearance of Canthans, and may have ties to the Emperor of Cantha - for by the Canthan government's request, they prevented you from "smuggling" Canthan goods to Tyria. (Though in reality, this was simply ArenaNet's way of saving the economy)