Mark Hurd, the man credited with reinvigorating Hewlett-Packard Co., resigned as chief executive of the technology giant after an investigation of his relationship with a female contractor found he violated the company's business standards.

H-P said Friday that Mr. Hurd, 53 years old, didn't violate the company's policy regarding sexual-harassment but submitted inaccurate expense reports that were intended to conceal what the company said was a "close personal relationship" with the woman.

The...