Bantam Books is an American publishing house owned entirely by parent company Random House, the German media corporation subsidiary of Bertelsmann; it is an imprint of the Random House Publishing Group. It was formed in 1945 by Walter B. Pitkin, Jr., Sidney B. Kramer, and Ian and Betty Ballantine. It has since been purchased several times by companies including National General, Carl Lindner's American Financial and, most recently, Bertelsmann; it became part of Random House in 1998, when Bertelsmann purchased it and merged it with Bantam Doubleday Dell. It began as a mass market publisher, mostly of reprints of hardcover books, with some original paperbacks as well. It expanded into both trade paperback and hardcover books, including original works, often reprinted in house as mass-market editions.
Source: Wikipedia, "Bantam Books", available under the CC-BY-SA License.