Adding Robin Hood to Greyhawk is easy.  Although it can be considered a Heresy.  The group has to be added where there is a forest.  And probably while a Crusade is going on.  It's also a good idea to pick up either GURPS Classic Robin Hood from Warehouse 23, or the Campaign Classics: Robin Hood for Rolemaster and Fantasy Hero.  The last is available second hand on Ebay.  You might also find Howard Pyle's work on Robin Hood a good read. 

If you want to delve deeper, there is a bibliography at the back of GURPS Classic Robin Hood that provides you a good starting point.

The following nations are good for adding Robin Hood.

Furyondy -- the nation of Furyondy currently (as of 591 CY) started a Crusade against the Empire of Iuz.  Belvor IV could be like King Richard I of England.  Unlike the Crusades of our world (they are complicated in History), Furyondy's Crusade against Iuz is a moral Crusade against a real evil.

 The Prince John character could be a brother or baron looking to expand his power.  Sir Guy of Gisbourne could be a knight that stayed behind to help guard Furyondy. Same with the Sheriff of Nottingham (just choose a Furyondy city or province that would work well)

Robin Hood could be based in the Vesve Forest.  He could be a highway man robbing from the rich to give to the poor.

The Duchy of Ulek -- The Duchy of Ulek has the Silverwood within it's borders.  A perfect place to place Robin Hood and his merry band.  

The duke of Ulek could be away for some reason, and a treacherous brother could fill what is needed for Prince John. The Sheriff of Nottingham becomes a Sheriff of what ever county in the Duchy of Ulek you need him to be. And Sir Guy would be part of a county of the Duchy.

The Duchy of Ulek was where I set Robin Hood for my own Robin Hood campaign.

There are other nations where you can set Robin Hood.  The Great Kingdom of Aerdy can be a good fit.  But the two places above are my suggestions for setting a Robin Campaign.  Reading through the Greyhawk Campaign Setting (circa 1983), the Living Greyhawk Gazetteer (circa 2001), or Greyhawk: the Adventure Begins (1998) and reading through various sources for Robin Hood can give you more ideas on how to fit Robin Hood within Greyhawk.

• Greyhawk Epic Level Guide

• DRAFT - A VERY ROUGH WORKING DRAFT

• Compiled and Edited by Rob Douglas

• Contributing Authors: Rob Douglas, 

• Based on original material by E. Gary Gygax, Carl Sargeant, Man of the Cranes, 

▾ Introduction

• With my own campaign encroaching on Epic Levels after the release of the Epic Level Handbook, I found myself wondering how these rules would impact the World of Greyhawk in particular.  In older editions of the game, characters above 20th level seemed to be beyond what could be reasonably represented in the game.  But with  the release of the ELH, I was inspired to begin cataloging my ideas for an epic Greyhawk campaign.  

• In this document I am attempting to gather D&D 3rd edition statistics for the Epic level features that have been introduced into the World of Greyhawk setting, as well as maintain links to details on elements of Greyhawk that are particularly Epic.  I also want to provide a collection of adventure and campaign ideas for Epic level play.

• Since it was first introduced, there have been elements of the World of Greyhawk which were even more spectacular, more magical, and more epic than the basic rules of the game could cover.  The Suloise Mages, the Twin Cataclysms, Iuz, Slerotin's Tunnel and innumerable artifacts, as well as the prospects of divine ascension, and interactions with the gods themselves, all call to mind elements more fantastic than the basic D&D rules can cover.  Carl Sargeant's work with Iuz the Evil, and Ivid the Undying extended many of these concepts, and others have written of Vecna, the Ur-Flan, and the Age of Myth.  And then there are the Gord novels, which definitely cover an epic level of interaction, including demon wars and ultimately the battle with Tharizdun.  Greyhawk is a campaign world rife with possibilities for characters who have surpassed the powers of even the famed Circle of Eight, those who can contend or conspire directly with Mordenkainen, et al.  I hope this work will help inspire such innovation, and continue to grow with more information to share with others.

• Chapter 1: Characters, Skills, and Feats

▾ Chapter 2: Epic Spells

• Iggwilv's Curse (Rot8)

• Invoked Devastation

• Rain of Colorless Fire

• Slerotin's Tunneling

▾ Chapter 3: Running an Epic Game in the World of Greyhawk

▾ The Epic Adventure

▾ Adventure Themes

• 1) Imprisoned Epic - something was imprisoned and now is about to escape or has escaped.

• 2) Strange lands - the world is not fully mapped or explored. While everyone [i]thinks[i] that the main land (the Flannaess) is the most advanced, maybe it is not.

• 3) Ancient Lore - Lost Epic lore from ages past comes to light. This is similar to Imprisoned, but tied more to historical events. The Elves, and the Suel both represent powerful, probably epic level cultures, and both have lost cities to the desert or demiplanes that could house epic items, spells, and/or monsters - or even NPCs.

• 4) Interplanar threats - once you look beyond this one world, epic things are more necessary to keep order in the multiverse. Greyhawk would be devestated by a gate opening that brought in thousands of demons. So being able to stop that gate at the source, and not disturb the balance of the world would be an epic challenge.

• 5) interplanetary threats - very similar, but slightly different. There was some work done on this in 2E with Spelljammer, but if you didn't use that, it opens up space travel as a truly Epic area of expertise. Perhaps stopping an invasion of devastation vermin from another planet would be a challenging task.

• Epic Dungeons

• Epic Wilderness

• Planar Travel

▾ The Epic Campaign

▾ Published Adventures Suitable for Epic Level play (pre-3E)

• The Apocalypse Stone

• The Dancing Hut

• Die, Vecna, Die!

• A Paladin in Hell - requires conversion, but is mostly extra-planar, and has Emerikol

• Return to the Tomb of Horrors

▾ Vortex of Madness

• Vortex of Madness

• The Black Acropolys

▾ Published Adventures Suitable for Epic Level play (3+E)

• Bastion of Broken Souls

• Adventure in ELH

• Dungeon 92: Raising of Redshore

• Dungeon 93: Storm Lord's Keep

• Dungeon ??: Githyanki Incursion

• Dungeon ??: Quicksilver Hourglass

▾ Site-Based Epic Adventures

• Darnakurian's Doom (Ivid)

• The Soul Husks (Iuz)

▾ Event-Based Epic Adventures

• The Avatars of Tharizdun (22 Questions)

• Foil the Old One

• Time-Travel to stop Dragon-Kings in -10000 to -7000 CY (Age of Myth)

• Epic Character Motivation in Greyhawk

▾ Demographics

• Planar Metropolises in Greyhawk

• Managing Wealth

• Divine Ascension

• 100 Epic Adventure Ideas

• Epic Encounters

• Rewards

▾ Chapter 4; Epic Magic Items

▾ Artifacts

• Minor Artifacts

▾ Major Artifacts (see Dragon #299)

• Cauldron of Night (Ivid)

• Causeway of Fiends (Ivid)

• Helm and Wand of Lynerden the Spinner (Ivid)

• Mace and Talisman of Krevell (Ivid)

• Malachite Throne (Ivid)

• Spear of Sorrow (Ivid)

• Unholy Bloodshield (Ivid)

• Dweornite

Iuz the Evil, pg 37

▾ Chapter 5: Epic Creatures

In this chapter, we will discuss how various Epic-level monsters and other sentient threats can be used in the world of Greyhawk.  As noted before, some adventures will likely take place on any of the various planes and demiplanes known to exist in the multiverse.  As a result, any creature could be used.  The goal here is to provide some Greyhawk-specific motivation for using these creatures.  First we will look at the 3rd edition Epic creatures, including some from the Monster Manual, Epic Level Handbook, and other 3E d20 sources.  There will also be a section detailing creatures from older editions that could be converted into Epic-level creatures in 3E.

• Monster Manual

▾ Epic Level Handook

▾ Abomination

• Atropal

• Genius Loci

It may be that the god known as the Earth Dragon is actually a Genius Loci.  If so, it cannot directly grant spells, but could be working for an evil god who does, with the intention of undermining Beory's control of Oerth.

• Hunefer

The Hunefer is a mummy of an ancient god-like being.  In Greyhawk, these creatures could be used to represent imprisoned avatars of Tharizdun or other gods.  Defeating them might cause such beings to eventually escape their confines, even against the PCs desires.

Or they could be the remains found in the Soul Husks caverns, from which Iuz draws his power.  Defeating them would release that power from Iuz, resulting in a loss of Divine Rank and other abilities.

• Le Shay

It is possible that the Sentinels mentioned in Ivid, guaring the entrance to Darnakurian's Doom are actually Le Shay.  They are all that remains of the great elves of that time, when all of their kin were killed.  They are immortal but cannot breed, and their only goal is to prevent Hunger from ever being released.

• Book of Vile Darkness

• Book of Exalted Deeds

▾ Older edition conversion

• Emerald Green Man?

▾ Chapter 6: Greyhawk as an Epic Setting

• Epic Geography

▾ Epic Organizations

• The Sentinels (Ivid)

If this is a group of Le Shay, see that entry under Epic Creatures.  However, the Setinels may also be a goup of Epic Level elven wizards.  PCs may be asked ot join them, allowing them knowledge of the sword Hunger, and requiring them to protect it against groups of (evil?) adventurers seeking it.  It is reasonable to assume that there are other elven artifacts from the same time that the elves are eager to secure and protect against human invovment, and the PCs may take on the role similar to that of an Agent Retriever for the elves, to find and secure these items.

▾ Epic NPCs

While not all of the NPCs presented here are yet Epic-level, they are all powerful enough that they could become part of an Epic campaign and reach epic levels along with the PCs.  For this reason, I include many PCs of levels 15 and higher.  I also included they latest canonical class/level attached to each character, and my own conversion preference.  I use ECL for determining whom to include, as there are some powerful personages who are not of a standard race who do have an Epic effect on the setting.  In general, NPCs are grouped by their geography.

▾ Iuz

• Iggwilv, Wiz30 (Retof8, WG6,S4)

▾ Former Great Kingdom

• Goldwhite, Rog20+ (Ivid)

• Gwydiesin of the Cranes, Bard30+? (Ivid)

• Hierranea, Storm Giant, Clr13 (Ivid)

• Ivid, Animus, Clr7/Wiz14 (Ivid)

• The Specter (Ivid)

• The Walker (Ivid)

• Xaene, Lich, Wiz20+?

• Keoland

• Furyondy and Veluna

▾ Greyhawk Region

• Philidor, Wiz26+ (FtA:CB)

• Rary, Wiz25+ (Rary)

• Tenser, Wiz21+ (Retof8)

▾ References

• 22 Questions about Tharizdun, Gary Gygax

• Age of Myth, Man of the Cranes, 

• WGR5 Iuz the Evil, Carl Sargent

• Ivid the Undying, Carl Sargent

• Living Greyhawk Gazetteer, Erik Mona, 

• Return of the 8, 

▾ Appendix - Epic Resources

▾ Wizards Epic Forum

• boards1.wizards.com—forumdisplay.php

▾ EpicHawk Discussion Forum

• www.canonfire.com—modules.php

• http://boards1.wizards.com/leaving.php?destination=http://www.canonfire.com/cfhtml/modules.php%3Fname%3DForums%26file%3Dviewtopic%26t%3D1090

▾ DiceFreaks Epic Forum

• community.dicefreaks.com—index.php

▾ Maldin's Epic Mysteries

• melkot.com—epic.html

▾ Duicarthan's NPC Conversions

• www.geocities.com—npcz.html

▾ Immortals Handbook

• www.immortalshandbook.com

▾ Book of Immortals - Mongoose publishing

• www.mongoosepublishing.com—detail.php

• search.barnesandnoble.com—isbnInquiry.asp

▾ Legends of Avadnu

• www.rpgnow.com—product_info.php

• enworld.cyberstreet.com—index.php

The Suel are the best because they are.