Ted Koppel will sign off as the anchor of “Nightline” tonight, and the show will never be the same. In addition to all the kudos he’s earned in 25 years hosting that show (a total of 42 years at ABC), he’s also the only person in television I’ve ever seen who had the power to hijack an entire network.

While there are primetime shows that run “supersize” episodes, or are extended by the network a few minutes into the next show’s hour (a la “Lost” last week), and there are live events and games that go on past their scheduled end time, Koppel is the only newsman I ever saw announce — on the air — “Quick note to our affiliates, we’ll be going a little bit long tonight.” I always pictured some late-night engineer at an ABC affiliate having to scramble to change the automation, update commercial breaks, and push other late-night programming back even further into the night, not even sure of how long “a little bit” would last.

Koppel hasn’t done that for years for two reasons. One, he’s not there many nights, having long ago given up the five-night-a-week schedule. Two, “Nightline” has become a pre-recorded show, snugly fit into its assigned half-hour slot. After all, ABC now has other late night programming (“Jimmy Kimmel Live”) that makes money for the network.

ABC’s plans for the post-Koppel “Nightline” may include going back to the always-live format, but without Ted in the anchor chair to ask the tough questions and keep us interested, it won’t matter.