Angel
From ACT Wiki
A business angel investor uses their personal disposable finance and business or professional experience to invest in the growth of a small business, generally in start-up or early stage. By definition, all such businesses would generally be perceived as high risk.
Angel investors can make investments on their own or as part of a syndicate.
For example, the panel investors on the TV shows, Shark Tank and Dragons Den, would be classed as 'angel' investors.