Question: Who published a supplemental sourcebook to the core rules of the second edition of the "Advanced Dungeons & Dragons" designed by an American game designer at a company where he was employed for over fifteen years?
Context: In the "Dungeons & Dragons" fantasy role-playing game, the lamia is a type of fictional monster.  The lamia is typically portrayed in the game as a creature with the lower body of a lion, and the upper torso, arms, and head of a human female.  A less common type of lamia, the lamia noble, was depicted as having the lower body of a serpent.  The lamia was introduced in the first edition "Advanced Dungeons & Dragons" game's original "Monster Manual" sourcebook, written by Gary Gygax and published in 1977.  The lamia also appeared in second edition and third edition "Dungeons & Dragons".  In the fourth edition, it was reenvisaged as a swarm of insects.  The fifth edition disregards this and returns it to its classic design. The Dungeons & Dragons Adventure Game is the name of two companion accessories to the second and third editions of the "Dungeons & Dragons" fantasy role-playing game.  Designed as simpler, stand-alone versions of "Dungeons & Dragons", they feature a simplified ruleset, but with character progression that parallels the standard game.  However, for 3rd-level characters and higher, the standard "Player's Handbook" is still required.  The first version was published in 1999 for the second edition of "Advanced Dungeons & Dragons", while the second version was published in 2000 for the third edition of "Dungeons & Dragons". The Book of Artifacts (abbreviated as BoA) is a supplemental sourcebook to the core rules of the second edition of the "Advanced Dungeons & Dragons" fantasy role-playing game.  This book, published by TSR, Inc. in 1993, details 50 different "artifacts", special magic items found within the game at the Dungeon Master's option.  The book was designed primarily by David "Zeb" Cook, with some additional design by Rich Baker, Wolfgang Baur, Steve and Glenda Burns, Bill Connors, Dale "Slade" Henson, Colin McComb, Thomas M. Reid, and David Wise.  Cover art is by Fred Fields and interior art and icons were designed by Daniel Frazier. The Marklands is a sourcebook for the "Dungeons & Dragons" fantasy role-playing game that describes the realms of Furyondy, Highfolk, Nyrond in the game's "World of Greyhawk" campaign setting.  The sourcebook bears the code WGR4 and was published by TSR in 1993 for the second edition "Advanced Dungeons & Dragons" rules. Iuz the Evil is a sourcebook for the "Dungeons & Dragons" fantasy role-playing game that describes the realms of the evil demi-god Iuz in the game's "World of Greyhawk" campaign setting.  The sourcebook bears the code WGR5 and was published by TSR in 1993 for the second edition "Advanced Dungeons & Dragons" rules. Player's Option: Skills & Powers (abbreviated SP, or S&P) is a supplemental sourcebook to the core rules of the second edition of the "Advanced Dungeons & Dragons" fantasy role-playing game. Dungeon Master Option: High-Level Campaigns is a supplemental sourcebook to the core rules of the 2nd edition "Advanced Dungeons & Dragons" ("AD&D") fantasy role-playing game. Player's Option: Combat & Tactics (abbreviated CT, or C&T) is a supplemental sourcebook to the core rules of the second edition of the "Advanced Dungeons & Dragons" fantasy role-playing game.  This 192-page book was published by TSR, Inc. in 1995.  The book was designed by L. Richard Baker III and Skip Williams.  Cover art is by Jeff Easley and interior art is by Doug Chaffee, Les Dorscheid, Larry Elmore, Ken and Charles Frank, Roger Loveless, Erik Olson, and Alan Pollack. Book of Vile Darkness is an optional supplemental sourcebook for the 3rd edition of the "Dungeons & Dragons" role-playing game.  The book was written by Monte Cook and published by Wizards of the Coast in October 2002.  Described as a "detailed look at the nature of evil," it was the first "Dungeons & Dragons" book labelled for mature audiences.  The second was the "good" companion volume "Book of Exalted Deeds".  Another "Book of Vile Darkness" was published for the 4th edition of "D&D" in 2011. David "Zeb" Cook is an American game designer, best known for his work at TSR, Inc., where he was employed for over fifteen years.
Answer: TSR, Inc.