Question: Who designed The City of Greyhawk and goes by the pen name Keith Martin?

Context paragraphs:
Carl Sargent: Carl L. Sargent (born December 11, 1952, in Caerleon, Monmouthshire, Wales) is a British parapsychologist and author of several roleplaying game-based products and novels, using the pen name Keith Martin to write Fighting Fantasy gamebooks.

Let Me Take Control: Let Me Take Control is a Keith Martin album released on 13 August 2007 by Galaxy Records.  The song "Lady" was released as the first single.  This album is Martin's third Filipino album.

The City of Greyhawk: The City of Greyhawk is a boxed set accessory for the World of Greyhawk campaign setting, part of the "Advanced Dungeons & Dragons" fantasy role-playing game.  It was designed by Doug Niles, Carl Sargent, and Rik Rose, and published by TSR in 1989.  It describes the Free City of Greyhawk (the major city of the campaign setting) in detail, and was highly praised by "Dragon" magazine.

Greyhawk: Greyhawk, also known as the World of Greyhawk, is a fictional world designed as a campaign setting for the "Dungeons & Dragons" fantasy roleplaying game.  Although not the first campaign world developed for "Dungeons & Dragons"—Dave Arneson's "Blackmoor" campaign predated it by over a year — the world of Greyhawk was the setting most closely identified with the development of the game from 1972 until 2008.  The world itself started as a simple dungeon under a castle designed by Gary Gygax for the amusement of his children and friends, but it rapidly expanded to include not only a complex multi-layered dungeon environment, but also the nearby city of Greyhawk, and eventually an entire world.  In addition to the campaign world, which was published in several editions over twenty years, Greyhawk was also used as the setting for many adventures published in support of the game, as well as for RPGA's massively shared "Living Greyhawk" campaign from 2000–2008.

Jane Thayer: Jane Thayer (the pen name of Catherine Woolley, August 11, 1904 – July 23, 2005) was an American writer.  She is known best for the book "The Puppy Who Wanted A Boy", which became the basis of a 1980s Saturday Morning cartoon series, "The Puppy's Further Adventures".  Jane Thayer wrote 86 books for children, many of which ("The Blueberry Pie Elf" and "The Puppy Who Wanted a Boy for Christmas") have become classics.  She was so prolific that her editor suggested she publish some of her works under a pen name.  Thus, Catherine authored picture books under the pen name of Jane Thayer, while writing books for older children and adults under her real name.

Free City of Greyhawk: The Free City of Greyhawk, also known as Greyhawk City and the "Gem of the Flanaess," is a fictional city-state in the "World of Greyhawk" campaign setting for the "Dungeons & Dragons" fantasy roleplaying game.  Since the setting was originally published in a folio and then again in a boxed set that were both titled "World of Greyhawk", the word "Greyhawk" is often used to describe the entire campaign world setting, although the proper name for that part of the world is the Flanaess.  Sometimes the lands controlled by the Free City are also referred to as Greyhawk, though the proper term for the region is the Domain of Greyhawk.

Keith &quot;Wonderboy&quot; Johnson: Keith Lamar Johnson (born May 17, 1972), who goes by the stage name Keith "Wonderboy" Johnson, is an American gospel musician.  He started his solo music career, in 1998, with the release of, "Through the Storm", that was released by World Wide Gospel Records.  He has released fourteen albums, over the course of thirteen years, with World Wide Gospel Records, Worldwide Records, Verity Records, Central South Records, and Blacksmoke Records.  Eleven albums have charted on the "Billboard" magazine Gospel Albums chart with other chartings on the Independent Albums and Heatseekers Albums charts.

Keith Martin (heavy person): Keith Martin (1969 or 1970 – December 5, 2014), one of the world heaviest lived people, was famous for being at one point the UK’s heaviest man, weighing approximately 980 lbs at his peak.  Keith Martin was given a gastric bypass operation by the NHS, and had lost over 50% of his body weight.

Colin Falconer (writer): Colin Falconer (born 1953) is a pen name of Colin Bowles, who also uses the pen name Mark D'Abranville, an English-born Australian writer.  Works published under the pen name include contemporary and historical thrillers, and children's books.  Under his original name he has also published books of satirical fiction; non-fiction books about language; television and radio scripts; and many magazine articles and columns.

Agnez Mo: Agnes Monica Muljoto (born 1 July 1986), known by her stage name Agnez Mo, is an Indonesian singer-songwriter, and actress.  Born in Jakarta, She is currently the richest celebrity of Indonesia.Agnez started her career in the entertainment industry at the age of six as a child singer.  She has recorded three children's albums and became a presenter of several children's television programs.  In 2003, Mo released her first adult album entitled "And the Story Goes", which catapulted her name back in the Indonesian music industry.  Mo's success in homeland encouraged her to set a target to get a career in the international music scene.  On the second album released in 2005, "Whaddup A.. ' ?! ", she collaborated with American singer Keith Martin for single "I'll Light a Candle".  Mo also took part in two Taiwanese drama series, "The Hospital" and "Romance In The White House".

Supporting paragraphs: The City of Greyhawk Carl Sargent
Answer: Carl Sargent