In the end, Paul Singer did what Carl Icahn couldn’t: Got Mentor sold.

Singer, the hedge fund manager known for taking large positions in companies and pushing for tough changes, breakups or sales, started accumulating shares of the EDA CAD company earlier this year. In September, it was revealed that his company Elliott Management, had bought up 8.1% of Mentor’s stock. Elliott immediately started lobbying for changes.

For Mentor, it could have seemed like a recurring bad dream. The company had been through this before, starting six years ago, when Carl Icahn, himself a famed corporate raider, began acquiring shares and issuing accusations of waste throughout the organization.

Icahn’s relationship with Mentor was public and acrimonious. Soon others joined the fray. Everything went under the microscope, from spending on marketing to the personal wealth of the directors. CEO Wally Rhines came under attack for pocketing $65 million from Mentor while the company generated only $113 million in free cash between 2001 and 2011. Icahn even offered to buy the company outright for $1.9 billion, a figure Mentor’s board dismissed as too low.

The board, however, couldn’t outright avoid Icahn and the others, who at their peak owned more than 20% of the company. Instead, they executed a “poison pill” amendment to its bylaws, making a hostile takeover more expensive and risky.

Icahn managed to land three directors on Mentor’s board but never affected the breakup or sale he had hoped for. Mentor bought back half his shares in February for $146 million, and he sold the last of his holdings in May.

Icahn certainly made a pile of money off Mentor. It took Singer, however, to fundamentally change the trajectory of the company.

Upon Elliott’s announcement, Mentor charted a different course. Instead of waging another attempt to fend off the barbarian at the gate, this time it signed on with Bank of America as an advisor to a possible sale. The deal with Siemens came quickly thereafter.

Singer’s stance was Mentor was undervalued by 20%. The price Siemens is paying — $4.5 billion — suggests even he was low.

Siemens was never a stretch as a suitor. As far back as 2011, we suggested the German conglomerate was one of a few companies that made sense to possibly acquire Mentor.

For some involved, the deal completes a circle. Mentor will become part of Siemens PLM, whose president Tony Hemmelgarn is a former Integraph executive. In fact, he was director of sales and marketing when the company spun off its Electronics Division into a wholly owned subsidiary known as VeriBest. Mentor then acquired VeriBest for $19 million in 1999.

It does spell the end to Mentor after 35 years as a standalone company. Founded by a trio of Tektronix engineers — Tom Bruggere, Gerry Langeler and Dave Moffenbeier — in 1981, Mentor added the PCB division through a merger with CADI in 1983. (Just after, Mentor hired the legendary John Cooper, who with partner David Chyan eventually developed the first shape-based router.)

In all likelihood this also means an end to Wally Rhines’ 23-year tenure as head of Mentor. He will be remembered as a steady leader during a period of great upheaval and M&A in EDA. On his watch, Mentor’s revenues grew from $340 million to nearly $1.2 billion. That’s a pretty darn good run.

Less clear is how the rest of the industry will react. Siemens gives Mentor exceptionally deep pockets, a buffer against meddling shareholders, and an extensive market for technology both as a customer and to partner with. The focus on “concept to system” just got a big boost.

By comparison, on the PCB side, the door has been slammed shut on one of the exit strategies for Cadence and Altium. Dassault has been rumored to be kicking the tires on Altium; this could trigger a move. Will PTC, which shares a Boston area neighborhood with Cadence, be compelled to act as well in order not to get shut out of ECAD? As one longtime industry observer noted to me recently, “It’s about the form factor.” OEMs want to design product in its entirety, not in silos of electrical, electronics, mechanical and wire harness. Given that, it’s a safe bet the M&A in ECAD won’t stop with this deal.