PlayStation inventor Ken Kutaragi officially left Sony on Tuesday, leaving behind a franchise struggling against increasing competition from the Nintendo Wii and Microsoft Xbox.

Kutaragi had said in April that he would retire on June 19 as chairman and group chief executive of Sony Computer Entertainment. However, the announcement still came as a surprise to many observers in the consumer electronics industry.

In an interview in April with CMP publication EE Times, Kutaragi said he already had turned over his vision for PlayStation over the next two years to design teams. The future of the PlayStation was tied to the Internet and online gaming, he said.

As to his future, Kutaragi said he would maintain an amicable relationship with Sony, but his future projects would be largely independent of the consumer electronics company.

Since hitting the market seven months ago, PlayStation sales have been outpaced by Nintendo's Wii and Microsoft's Xbox 360. The former led in video game console shipments in April for the fourth consecutive month, with shipments quadrupling PlayStation 3 and more than doubling Xbox shipments, according to The NPD Group.

While considerably less expensive and technically less advanced than the PlayStation 3, the Wii's motion-sensitive control, which lets the user simulate playing golf, tennis, and other activities in games, has proven extremely popular with gamers.

The PlayStation 3's debut in the United States and Japan last November arrived six months later than expected, due to technical delays. The video game console's debut in Europe also was pushed back.