Thief

Description
Thieves are a part of Explorers, they are short-medium range characters mostly using daggers, claws and throwing stars. They are the fastest short range attackers in the game, dealing weak yet many attacks on a foe. They use their natural quickness and agility to navigate the area, trying to gain the upper hand. Generally, Thieves have the highest avoidability and second highest accuracy in the game. Playing them is also quite expensive, especially Assassins that are required to continuously re-charge stars. 

First Job Advancement
Once a Beginner reaches level 10, he/she can travel to Kerning City, and enter the Thieves' Hideout. Speak to the Dark Lord and the Beginner will become a Rogue.

Second Job Advancement
Once a Rogue reaches level 30, he/she can return to Kerning City and talk to the Dark Lord, he will give you a letter to pass on to the Thief Job Instructor, once giving him the letter, the Rogue will be teleported to another map with the errand to collect 30 Dark Marbles from the enhanced monsters inside.

Once obtain the Dark Marbles, talk to the Thief Job Instructor again and he will give the player the Proof of Hero. Take the Proof of Hero to the Dark Lord in Kerning City to advance to either an Assassin or Bandit.

Assassin
Assasins are users of Claws & Shurikens/Ninja stars. The are alike Bowmen in a sense that they need a supply of ammunition. Unlike Bowmen, Assasins have a variety of different kinds of ammo which don't often from most foes but some can still be bought. They are also the most common job in Maplestory.

Bandit
Bandits are close range fighters which use Daggers & Cutters. Bandits have weaker attacks compared to Warriors but are also faster than them. They are more in danger due to having to get up close & personal but don't have to worry about funding as much.

Third Job Advancement
Return to Dark Lord and exchange the Necklace of Power for a Necklace of Strength. Return to El Nath and give the item to Arec.Once an Assassin or Bandit reaches Level 70, he/she could go to Chief's Residence in El Nath and speak to Arec. After talking to Arec, head to Victoria Island and talk to Dark Lord who is located at Kerning City. Find the Door of Dimension located at Prohibited Altar in Sleepywood and it'll bring you to The Path of the Glittering Crystal. Defeat Dark Lord's Clone and retrieve the Necklace of Power.

Head to Holy Ground at the Snowfield and answer 5 questions (With the payment of one Dark Crystal every time you fail to answer every question correctly) to obtain the Necklace of Wisdom.

Head back to Arec in El Nath and give him the Necklace of Wisdom and the character will be advanced either to a Hermit or Shadower.