The d20 System is a role-playing game system published in 2000 by Wizards of the Coast, originally developed for the 3rd edition of Dungeons & Dragons. The system is named after the 20-sided dice which are central to the core mechanics of many actions in the game. Much of the d20 System was released as the System Reference Document (SRD) under the Open Game License (OGL) as Open Game Content (OGC), which allows commercial and non-commercial publishers to release modifications or supplements to the system without paying for the use of the system's associated intellectual property, which is owned by Wizards of the Coast. The original impetus for the open licensing of the d20 System involved the economics of producing role-playing games (RPGs). Game supplements suffered far more diminished sales over time than the core books required to play the game. Ryan Dancey, Dungeons & Dragons' brand manager at the time, directed the effort of licensing the new edition of Dungeons & Dragons through the d20 System Trademark, allowing other companies to support the d20 System under a common brand identity. This is distinct from the Open Game License, which simply allows any party to produce works composed of or derivative of designated Open Game Content. Mechanics The d20 System is a derivative of the third edition Dungeons & Dragons game system. The three primary designers behind the d20 System were Jonathan Tweet, Monte Cook, and Skip Williams; many others contributed, most notably Richard Baker and Wizards of the Coast then-president Peter Adkison. Many give Tweet the bulk of the credit for the basic resolution mechanic, citing similarities to the system behind his game Ars Magica. Tweet, however, stated "The other designers already had a core mechanic similar to the current one when I joined the design team". To resolve an action in the d20 System, a player rolls a 20-sided die and adds modifiers based on the natural aptitude of the character (defined by six attributes: Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma) and how skilled the character is in various fields (such as in combat), as well as other, situational modifiers. If the result is greater than or equal to a target number (called a Difficulty Class or DC) then the action succeeds. This is called the Core Mechanic. This system is consistently used for all action resolution in the d20 System. In prior games in the D&D