Betting runner who places bets for professional bettors so that they can hide their identity from bookmakers.
Several reasons make someone use a beard rather than just placing a bet themselves. 

Here are a few of the most common:

It is possible for a player who has been banned from one betting website or retail betting shop to use a beard to place wagers for them. Perhaps this particular bookmaker offers the most competitive odds, or an unusual type of bet, or a sport that can’t be found anywhere else. 

As a rule, if you are involved in a particular sport at a certain level (players, coaches, officials, etc) you are not allowed to bet on it. The same applies to the staff at bookmakers. The repercussions of getting caught would be quite severe, but if one of these people desperately needed to place a wager, they could use a beard. 

The local resident may not want to be seen placing a wager against his or her home team. They could use a beard who is an out-of-towner and wouldn’t be recognised. 

Most betting companies have limits on their games and sportsbooks. For example, if someone wanted to make a £30,000 wager but could only stake £15,000, he or she could hire a beard to make the other $15,000 wager. 
Many betting companies have a list of restricted countries where you aren’t allowed to bet online. If someone living in one of these countries wanted to place an online wager, they could hire a beard in an unrestricted country to place bets for them.