Was that their primary business?

Yes, the primary linear business, although I think the digital portion (RTL and DTL) was still much larger. For the linear, op amp was king. So they figured that if I designed a circuit that replaced one or two op amps, that would cut into their sales.

How did the 555 name come about?

Signetics had “500” numbers, and the earlier product I worked on was the 565, 566 and 567. It was just arbitrarily chosen. It was Art Fury (Marketing Manager) who thought the circuit was gonna sell big who picked the name “555”.

I wonder how many of these have been made?

At the moment, it is about 1 billion devices a year. These are mostly made in Korea now, Samsung. The electronics industry is big now.

Are there other chips with this kind of popularity?

You could say that the op amp is bigger, but there are so many different op amps, they have to specialize – there is no perfect op amp, so you optimize it, for different parameters. There must be 500 different op amp types.

The first ones were plastic or metal?

Both, simultaneously.