Most dangerous mosquito
Who
Unknown
What
50 percentage
Where
Africa
Malarial parasites of the genus Plasmodium carried by mosquitoes of the genus Anopheles have probably been responsible for 50% of all human deaths since the Stone Age (excluding wars and accidents).  Each year in sub-Saharan Africa alone 1.4-2.8 million people die from malaria.

Not only does Malaria kill, it also imposes a huge economic burden. According to the WHO, Africa loses $12 billion per year in lost production (Economist article 27/9/03, p.102).

Body length: 3 mm, weight: 0.002 g, lifespan: 17.5 days, discovered: 1902.