Jeffrey Skilling, former Enron CEO is serving 24 years.
However, there is a strong argument to be made that ever since Enron, the SEC has been defanged.
Taking a brief look at their list of accomplishments, it seems that these days, they just levy fines, instead of jailing criminals. [2][3] (Contrast the punishments for the financial crisis, vs low-level insider trading. The companies involved in the former pay fines, the people involved in the latter go to jail.)
[1] https://en.wikipedia.org/wiki/Enron_scandal
[2] https://www.sec.gov/spotlight/enf-actions-fc.shtml
[3] https://www.sec.gov/spotlight/insidertrading/cases.shtml