What do Mao Zedong , Adolf Hitler and Osama bin Laden have in common? Besides being mass murderers, all three have been featured as human spermatozoa in a German advertisement for condoms and safe sex. It's not clear what prompted advertising agency Grey Worldwide to come up with the controversial ad campaign for DocMorris pharmacies, but it had received enough complaints that it had to issue a formal letter of apology to the Chinese consulate in Frankfurt. The Chinese blogosphere has been set ablaze, with some threatening similar campaigns to ridicule German Chancellor Angela Merkel - the first female chancellor - as a sperm cell. Not sure that would work. Many Chinese residents in Germany have also been upset. But not everyone finds the ads offensive. An elderly netizen wrote in the popular website, Sina.com: 'I am a former worker who is now 70. I have thought about it a lot and I still cannot understand why these people defend Mao so strongly.' Last year, French carmaker Peugeot Citroen also had to apologise for using an advert in Spain that showed Mao as a cross-eyed old man.