A character class is a fundamental part of the identity and nature of characters in the Dungeons & Dragons role-playing game. A character's capabilities, strengths, and weaknesses are largely defined by their class; choosing a class is one of the first steps a player takes to create a Dungeons & Dragons player character. A character's class affects a character's available skills and abilities. A well-rounded party of characters requires a variety of abilities offered by the classes found within the game. Dungeons & Dragons was the first game to introduce the usage of character classes to role-playing. Many other traditional role-playing games and massively multiplayer online role-playing games have since adopted the concept as well. Dungeons & Dragons classes have generally been defined in the Player's Handbook, one of the three core rulebooks; a variety of alternate classes have also been defined in supplemental sourcebooks. Classes by type Principal base classes These classes have appeared as character classes in the core books of multiple published editions: Barbarian Bard Cleric Druid Fighter Monk Paladin Ranger Rogue Sorcerer Warlock Wizard Alternative base classes While the main character classes available have remained fairly consistent since the 1st edition of Advanced Dungeons & Dragons, a variety of alternate base classes have been offered in supplemental books. The release of Unearthed Arcana in 1985, for instance, introduced the base class of Barbarian and reworked Paladins to be a type of the new base class "Cavalier". Oriental Adventures also introduced a number of alternate classes more appropriate for an Eastern setting. The 2nd edition added several completely new base classes (e.g. Runecaster and Shaman); in addition, supplemental handbooks offered a variety of "kits" to customize each base class, and the Dungeon Master's Guide offered rules for creating new character classes. The 3rd edition introduced five classes for use in creating non-player characters in its Dungeon Master's Guide. Non-core base classes are considered optional and do not always exist in all settings. For example, the Samurai class introduced in the Oriental Adventures book may not make sense in a game set in a standard European-style realm. Similarly, classes associated with psionics such as the Psychic Warrior do not apply to worlds without psionics. Multiclassing Most editions of Dungeons & Dragons have allowed for the possibility to either advance in more than one class simultaneously, alternately taking levels in more than one class, or branching out in a