Andreas Bechtolsheim doesn’t like to waste time. The entrepreneur made one of the most celebrated investments in the history of Silicon Valley — the initial $100,000 that bankrolled a search engine called Google

in 1998 — while on the way to work one morning. It took just a few minutes.

Twenty one years later, Mr. Bechtolsheim may have seized a different kind of opportunity. He got a phone call about the imminent sale of a tech company and allegedly traded on the confidential information, according to charges filed by the Securities and Exchange Commission. The profit for a few minutes of work: $415,726.

The history of Silicon Valley is full of big bets and abrupt downfalls, but rarely has anyone traded his reputation for seemingly so little reward. For Mr. Bechtolsheim, $415,726 was equivalent to a quarter rolling behind the couch. He was ranked No. 124 on the Bloomberg Billionaires Index last week, with an estimated fortune of $16 billion.

Last month, Mr. Bechtolsheim, 68, settled the insider trading charges without admitting wrongdoing. He agreed to pay a fine of more than $900,000 and will not serve as an officer or director of a public company for five years.

Nothing in his background seems to have brought him to this troubling point. Mr. Bechtolsheim was one of those who gave Silicon Valley its reputation as an engineer’s paradise, a place where getting rich was just something that happened by accident.

“He cared so much about making great technology that he would buy a house, not furnish it and sleep on a futon,” said Scott McNealy, who joined with Mr. Bechtolsheim four decades ago to create Sun Microsystems, a maker of computer workstations and servers that was a longtime tech powerhouse. “Money was not how he measured himself.”