Exactly Who or What Assembles Transactions into Blocks? Users broadcast transactions into the network.  Miners find and compete to validate blocks created every ten minutes by combining transactions.  Who or what assembles the transactions into blocks every ten minutes?

Related: Setting the required number of leading 0s for the winning hash throttles the speed at which blocks, and therefore transactions, are validated.  Who adjusts that number?
Who or what assembles the transactions into blocks every ten minutes?


Miners do. They do this before they attempt to find a block solution. It's the reason that miners exist.


  Setting the required number of leading 0s for the winning hash throttles the speed at which blocks, and therefore transactions, are validated. Who adjusts that number?


The protocol defines how it should change. Each node works out the current difficulty independently, and each of them comes up with the same answer.