Example Solidity contract with an owner field

owner.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

/**
 * @title Owner
 * @dev Set & change owner
 */
contract Owner {

    address private owner; // the "owner" of the contract
    uint256 number;

    // event for EVM logging
    event OwnerSet(address indexed oldOwner, address indexed newOwner);

    /**
     * @dev Set contract deployer as owner
     */
    constructor() {
        owner = msg.sender; // 'msg.sender' is sender of current call, contract deployer for a constructor
        emit OwnerSet(address(0), owner);
    }

    function changeOwner(address newOwner) public {
        require(msg.sender == owner, "Caller is not owner");
        emit OwnerSet(owner, newOwner); //
        owner = newOwner; // update the owner
    }

    function getOwner() external view returns (address) {
        return owner;
    }

    function store(uint256 num) public {
        require(msg.sender == owner, "Caller is not owner");
        number = num;
    }

    function retrieve() public view returns (uint256){
        return number;
    }
}