Not content with trying to scuttle Michael Dell’s plans to take the world’s #3 PC maker private again, activist investor Carl Icahn has suddenly made a huge play for Apple as well. According to the Wall Street Journal, 77-year old Icahn claims to have taken a “large position” in Apple, causing a huge kerfuffle with analysts specualting on whether his involvement is good news or bad news for the company.

Icahn announced his latest gambit on Twitter, declaring:

We currently have a large position in APPLE. We believe the company to be extremely undervalued. Spoke to Tim Cook today. More to come.

— Carl Icahn (@Carl_C_Icahn) August 13, 2013

Icahn is well known for his outspoken nature, and his involvement in Apple – however it plays out – is sure to be eventful. At this point his intentions are unknown, but what we do know is that his most recent dabblings in technology giants have gotten a bit messy. Icahan famously took a large position in Yahoo a few years back, and immediately declared war on CEO and co-founder Jerry Yang, seeking to oust him and drive the company into bed with Microsoft. This effort ultimately failed, but it didn’t deter Icahn from trying it on over at Dell, where he’s currently embroiled in a struggle with CEO and founder Michael Dell, attempting to block his plans from taking the company private.

Apple, being a publicly traded company, can do nothing to prevent investors like Icahn from buying its stock. But does its management have anything to fear this time round?

Early indications are that Apple investors see Icahn’s move as a positive step, with the company’s share price rising by around 4% since he made the above announcement. Currently Apple’s stock is about $100 more than its one year low of $385.10, however it remains 8% down for the year. As for Tim Cook, Apple’s current CEO, he has publicly welcomed Icahn into the fold, with a spokesperson for the company saying that “we appreciate the interest and investment of all our shareholders. Tim had a very positive conversation with Mr. Icahn today.”

Maybe they did, and maybe Icahn and Cook can get along like a house on fire, but there are worries about the Apple’s performance over the last year that could prove damaging to any long-term relationship the men have.

Apple’s share price has been affected by fears that the company won’t be able to hold onto its position as the world’s most prosperous and innovative tech firm in the post Steve Jobs era. Just recently, Larry Ellison of Oracle joined in the criticism of Apple when he stated his belief that the company would soon go into a decline, describing Jobs as someone who could never be replaced.

“(Jobs was) our Edison, our Picasso,” explained Ellison.

If Cook is unable to turn Apple’s fortunes around, there’s a possibility that Icahn might attempt to oust him. Already, the billionaire investor has put forward some ideas on how Apple can bolster its fortunes, suggesting that the company expand its buyback program that it announced last year. The program started with $10 billion of shares being offered up, with an additional $60 billion made available the following quarter.

While there’s no suggestion yet that Icahn has anything disruptive in mind, the investor’s history would certainly point to some kind of action being taken if Apple can’t turn itself around soon.