From Diablo Wiki
The Hellfire Ring is a legendary ring created by crafting materials obtained via the Infernal Machine event. It was added to the game in Patch v1.0.5 and serves as an end game incentive for many players.
The Hellfire Ring is account bound and can not be traded, sold, or given away. It can only be earned via the Infernal Machine quest, so players who want one must find their own.
 Obtaining a Ring
Creating a Hellfire Ring requires multiple steps. Refer to the Infernal Machine article for full details, but briefly:
- Obtain the three keys and the Infernal Machine plan for the Blacksmith.
- The Key of Destruction will drop from Odeg the Keywarden in Act I - Fields of Misery
- The Key of Hate will drop from Sokahr the Keywarden in Act II - Dahlgur Oasis
- The Key of Terror will drop from Xah'Rith the Keywarden in Act III - Stonefort
- The Blacksmithing Plans will drop from Nekarat the Keywarden in Act IV - Silver Spire Level 1
- Craft three keys, one of each, into the Portal Device.
- Activate the Portal Device inside of the Heretic's Abode to create a red portal to one of the three Realms:
- Take the three demonic organs to Covetous Shen and craft them into a Hellfire Ring.
Note that steps 1-3 must be repeated multiple times, since you must create at least three red portals to obtain all three demonic organs. Furthermore, unless you are playing on Monster Power 10, the keywardens do not always drop keys and the uber bosses do not always drop the demonic organs
 Hellfire Ring Stats
You can buy the Hellfire Ring plan from Squirt the Peddler in Act 2 for 2 million gold. Take the plan to your Jeweler who needs to be level 10 to learn it. Once learned he will need all three of the above components and 50,000 gold to craft one Hellfire Ring.
He can craft one of four varieties of the ring where one of the affixes is guaranteed to spawn with +170-200 to a single attribute, either Strength, Dexterity, Intelligence or Vitality. The full ring stats are as follows:
- +170-200 to one Attribute.
- Increase Bonus experience by 35%
- Chance to launch an explosive ball of Hellfire when you attack.
- 4 random properties
- 170-200 Intelligence, Strength, Dexterity or 100 Vitality (you choose which one)
- You can only wear one Hellfire Ring. Your Followers can wear one also.
- There is no level requirement on the ring so any of your characters can wear it.
Sample Hellfire Rings.
- Look over Hellfire Rings crafted by the community.