AT&T Alive
The Bell System parent — broken up by antitrust decree in 1984, reassembled in pieces. Its research arm, Bell Labs, gave the world the transistor, Unix, and C.
Incorporated in 1885 to build the long-distance network, AT&T operated a regulated monopoly — 'Ma Bell' — until the 1982 consent decree split it into the Baby Bells (1984). The pieces have since largely merged back into the current AT&T Inc., legally a renamed Southwestern Bell.
For computing history, AT&T matters almost entirely through Bell Labs: the transistor (1947), information theory (1948), Unix (1969), C (1972), and the laser.