London, July 14 : Toivo Annus, one of the founding Estonian IT engineers who helped develop the global communication application Skype has passed away at the age of 48, the media reported. Annus, who had been backing startups around the world succumbed on 12 July to an "unexpected illness", according to a press statement issued by his widow on Monday. "I inform you with the utmost sadness that last weekend, on 12 July, our beloved husband, dad, entrepreneur and investor, Toivo Annus, succumbed to an unexpected illness," his widow was quoted as saying in the statement by online magazine Estonian World. Founded in 2003 by Janus Friis and Niklas Zennstrom, Skype was developed by four Estonian developers -- Ahti Heinla, Priit Kasesalu and Jaan Tallinn, besides Annus, said the report. Annus, who played a crucial role in managing the first Skype office in Tallinn, also oversaw the engineering team, it added. eBay acquired Skype in 2005 for $2.6 billion. With the proceeds of the sale, the four Estonian developers set up Ambient Sound Investment, a private asset management company. According to a report in DealStreetAsia, Annus became a prominent angel investor in Southeast Asia. Among the startups he had backed included Singapore's Red Dot Payment and Indonesian social dining directory Qraved. Skype became a part of Microsoft in 2012. Microsoft has said it would continue to invest in Skype that has crossed 40 million daily active users. Purchased for $8.5 billion, Skype communication tool has failed to keep up with other messaging rivals to date, while Microsoft Teams has seen a meteoric rise as millions of people work from home. /IANS