ens-usernames/contracts/common/Controlled.sol

pragma solidity ^0.4.23;

contract Controlled {
    /// @notice The address of the controller is the only address that can call
    ///  a function with this modifier
    modifier onlyController { 
        require(msg.sender == controller); 
        _; 
    }

    address public controller;

    constructor() public { 
        controller = msg.sender; 
    }

    /// @notice Changes the controller of the contract
    /// @param _newController The new controller of the contract
    function changeController(address _newController) public onlyController {
        controller = _newController;
    }
}