Without a doubt, however, it is Hans’s design work on the 555 integrated circuit in the early 1970s that has ensured him a prominent position in the history of IC technology. If you are or have been a practicing electrical engineer anytime in the last 40 years, then most likely you have used the 555 timer/oscillator chip in your designs. Since the introduction of the 555 by Signetics in 1972, this integrated circuit has outsold all other IC types by a wide margin, with over 1 billion units sold worldwide in 2003 alone. The design has continued unchanged for over three decades and the range of applications has spanned such diverse areas as children’s toys and space craft electronics. This Oral History will discuss Hans’s pioneering 555 design and the legacy of this historic integrated circuit.