New
#11
Within the router's web based interface, try clicking on each item in the left pane (and if need be, making selections in the right pane) to see if you can find a list of devices that are connected to the router. It might have wording like DHCP table.
If you find something like that, then hopefully it will list device name, IP address and MAC address. You don't need to post the MAC address, just look it up using the link that I posted. Doing that might let you know the manufacturer of the device... or at least the manufacturer of the network interface adapter.
If we cannot locate this device name TOM, then you might want to use the router's MAC filtering (shown in your screenshot) to allow only your known devices.