Every league should have a commissioner who is responsible for the day-to-day running of the league.
When fantasy leagues were first started, this job was a massive undertaking, with a lot of number-crunching from box scores in newspapers. The internet caused an explosion in fantasy baseball because this job became a lot easier. Statistics services formed, and now many sites totally run individual fantasy leagues using easily customizable rules.
Most commissioners now just manage the money, and any disputes that might come up within the league about trades and setting rules for transactions.

