There are three bosses that spawn in Hellgate. They are the Rotworm Queen, The Evil Eye, and Zevelon Duskbringer.
As far as we know The Evil Eye isn't worth killing. It doesn't drop any special items.
Rotworm Queen
The Rotworm Queen can be found here. There are only Rotworms around so you could leave a low level character with a stealth ring and be able to logout immediately if it wasn't there. You should able to kill it at a low level as it isn't that strong.

The Evil Eye
The Evil Eye can be found to the north eastern part of the Bonelord area. You could leave a character in many places around here.

Zevelon Duskbringer
Zevelon Duskbringer is found right by the entrance to Hellgate when you take the teleporter from Ab'Dendriel. You can park a noob character there with a stealth ring and may be able to find an area where you can logout but there are Ghouls that could give you the logout block. There are also skeletons and demon skeletons in the area. Your best bet here is to just leave a low level character with stealth rings and let the boss kill it. Then run on your main character to kill the boss.
