The story
Founded by Walter Annenberg in 1947.1
Upon his father's death in 1942, Walter Annenberg assumed responsibility for Triangle which had been formed from the assets and properties of the Cecelia Corporation, a company founded by his father, Moses Annenberg, in 1923, and named for his mother, Sarah "Sadie" Cecelia Annenberg. Cecelia Corporation's assets at the time included the Daily Racing Form, the Morning Telegraph in New York City, and The Philadelphia Inquirer, a daily newspaper based in Philadelphia. At the time Walter and his sisters inherited Triangle in 1942 it was worth $4 million.
In 1944 Annenberg started Seventeen magazine, which his sister Enid Haupt edited. In 1953 he started TV Guide which was the best-selling magazine in the country in the 1960s. It later started or acquired other publications, including Armstrong Daily, the Philadelphia Daily News, Good Food magazine, and Official Detective magazine.
In the 1950s Triangle began buying radio and TV stations including WFIL-AM-FM-TV in Philadelphia, WLYH-TV in Lancaster and Lebanon, Pennsylvania, WFBG-AM-FM-TV in Altoona and Johnstown, Pennsylvania, WNHC AM-FM-TV in New Haven, Connecticut, WNBF-AM-FM-TV in Binghamton, New York, and KFRE AM-FM-TV in Fresno, California.
Triangle owned cable TV operations in various regions including Suburban Cable TV Co. in suburban Philadelphia, Empire State Cable TV Co. in New York, and New Haven Cable TV Co. in Connecticut. It also owned ITA Electronics, a broadcasting equipment manufacturer based in Lansdowne, Pennsylvania, McMurray Printers, a small job press printer in Miami, McMurray Publishing Co., Ltd, which published the Canadian editions of TV Guide, Triangle Circulation, which handled the nationwide distribution of Triangle's magazines and those of other publishers, and Educasting, a developer of educational programming.
From Wikipedia’s article on Triangle Publications, shared under CC BY-SA 4.0.3