IPA: //ˈsteɪkər//
KK: /ˈsteɪkər/
A person who places a bet or wager, often in a gambling context.
The staker placed a large bet on the horse race.
Staker originates from the verb 'stake' (from Old English 'staca', meaning a post or pole) combined with the agent suffix '-er' (meaning a person who). A staker is a person who places a stake, often in a context of betting or investment.
Think of someone who places a 'post' ('staca') to mark their claim or investment — that's what a staker does.