Telefonica Deutschland Holding AG
A German telecommunications company (best known as O2) that runs one of the country's major mobile networks, selling phone, broadband, and data plans to everyday consumers and businesses across dozens of cities. It began in 1995 as VIAG Interkom, Germany's fourth mobile operator, then adopted the O2 name in 2002 and was later bought by Spain's Telefónica. Fun fact: the O2 brand is short for the oxygen molecule—chosen because mobile phones were seen as essential to life, just like the air we breathe.