An event which has come to be known as the Max Headroom broadcast signal intrusion occured on November 22, 1987 on two separate Chicago television stations.
The second hack came later that night, at 11:15PM local time. It was during a broadcast of Doctor Who on WTTW. This second intrusion lasted longer and included some difficult to understand speaking and strange actions. It’s probably best just to see it for yourself (keep in mind it’s NSFW):
This incident is famous today and has grown even moreso, thanks to the internet. Also, unless you believe one redditor, it remains unsolved to this day.