Seagrave Holmes

 is a merchant in Rivet City who runs Rivet City Supply in the Marketplace. He deals in random junk and weapons.

Unmarked quest: Council Seat
Bannon mentions that his council seat is being contested by Seagrave. He wants you to look for incriminating evidence against his opponent, which can be found in Seagrave's room (under the bed, leaning against the footlocker). The key for the room can be pickpocketed from Seagrave.

Once you have obtained the evidence, you have to side with either Bannon or Seagrave Holmes. Denounce the other to Lana Danvers and collect your reward. If you complete the mini-quest in Seagrave's favor, he will grant you a 10% discount on what he's selling and will buy what you're selling for 10% more.

The Wasteland Survival Guide
If you are working on the Wasteland Guide quest, he is one of the persons to talk to in finding out the History of Rivet City.

Appearances
 only appears in Fallout 3.