He was portrayed by the late John Ritter.
Ted Buchanan, often referred to simply as Ted, comes across as a sweet natured gentleman; as such he wins the heart of Joyce Summers, but not that of her daughter Buffy. Ted at first seems to act like a nice guy and tries to include Buffy into his new family as her potential new father. However, when Buffy begins to rebel, Ted starts to bully her (and show the darker side that he kept hidden from Joyce and Buffy’s friends), initially making it seem that she was just reacting badly to Ted’s intervening influence. It became clear that something was wrong with him when he threatened Buffy after he caught her cheating at a game of miniature golf.
One night, after Buffy comes home from a failed patrol at Sunnydale Park, she finds Ted in her room; Ted, knowing she had gone through his office at Lorrin Software, went into Buffy’s room, where he found her Slayer stuff and her diary, which contained information about her being the Slayer. Believing that Buffy is delusional, Ted tells her to toe the line, or else (as he puts it), he would show the diary to her mother and Buffy would “spend (her) best dating years behind the wall of a mental institution.”
The situation climaxes when Ted begins to leave the room with Buffy’s diary, and the two engage in a seemingly fatal battle, in which Buffy uses her Slayer strength on Ted and kills him.
Shocked at what she had done Buffy tried to reason both with herself and her mother, but was overcome with guilt. However, the nightmare was not over for her or Joyce, as Ted Buchanan miraculously returned — very much alive.
It was then his true nature was revealed; Ted was actually a deadly robot. His creator (who was also named Ted) was a sickly inventor in the 1950s, whose wife left him. The robot that Ted made was intended to be “a better Ted” (possibly the man he thought his wife should have for a husband). The robot then kidnapped Ted’s wife and held her captive in his bunker until she died. Ted seemed to inherit his creator’s personality, and would befriend women before murdering them if they “misbehaved.”
Buffy fought Ted again to save herself and her mother from the murderous machine, and managed to permanently destroy Ted — thus ending his threat for good.