Activist investor Trian Fund Management has taken a $900 million stake in cable TV and entertainment titan Comcast (CMCSA -1.10%). The hedge fund is best known for agitating for change at companies it targets, believing that shares are undervalued.

Trian's initial stake was confirmed by a securities filing that showed it accumulated nearly 7.2 million shares to close out the second quarter. Since then, that stake has grown to roughly 20 million shares (or roughly 0.4% of the company), according to a report Monday by The Wall Street Journal

Man pointing remote at a TV.

Image source: Getty Images.

"We have recently begun what we believe are constructive discussions with Comcast's management team and look forward to continuing those discussions," a Trian spokesperson said. 

Comcast stock hit all-time highs earlier this year, before the onset of the pandemic. Like many of its peers in the entertainment industry, several of Comcast's business segments have suffered as the result of stay-at-home orders and lockdowns.

NBCUniversal, which includes the company's movie studios and theme parks, has been particularly hard hit, with revenue from the two businesses falling 18% and 94%, respectively, in the second quarter. This pushed Comcast's overall revenue down nearly 12% during the same period. 

Another segment that has suffered as the result of the pandemic is European cable operator Sky, which Comcast acquired in late 2018 for roughly $39 billion. Some investors believed Comcast overpaid for the company after a protracted bidding war with Disney (DIS -0.02%). Sky's revenue declined 13% last quarter.

It's unlikely that Trian will gain sufficient leverage to force any big changes at Comcast. A recent regulatory filing shows that CEO Brian Roberts controls more than 33% of the total voting power of Comcast shares. 

Not everyone believes Trian's involvement will be good for shareholders. Barry Diller, chairman of IAC (NASDAQ: IAC) and Expedia Group (NASDAQ: EXPE), called Comcast "superbly" managed, while saying Trian's moves are typically "exploitative."