Michael Leisner, whose homophobic protest against food giant General Mills and their pro-marriage equality stance resulted in a viral video, died on Saturday after suffering a heart attack.

Mr Leisner’s protest – in which he ignited a box of Cheerios outside General Mills’ Golden Valley headquarters in Minnesota against the company’s opposition of the marriage amendment – was a huge viral Internet hit, not least because his stunt went wrong when he instead set the company’s lawn alight.

General Mills, the name behind many of world’s popular cereal brands, is the first major international organisation in the state to openly declare their opposition to anti-equality legislation, though they were preceded in this at the local level by St Jude Medical, which manufactures devices for health industry.

The anti-equality group, National Organisation for Marriage (NOM), which runs campaigns against marriage equality around the US, was quick to condemn the company for declaring “war on marriage.”

NOM, which currently boycotts Starbucks for their pro-equality stance, has also sent letters to 50 of the state’s largest companies, urging them to remain neutral on the measure.

According to his pastor, Dwight Denyes, Mr Leisner died from a heart attack while waiting to pick up his sons from tennis practice.

A statement released by his family said his sons found him in the car, not breathing.

A video taken of the protest by Mr Leisner’s friends was posted online and “caused a sensation among the LGBT blogosphere.” The video was shown on US programmes the Daily Show and Chelsea Lately.

According to The Huffington Post, the video also sparked off a police investigation, which has now been closed following Mr Leisner’s death.