This looks like a male Steatoda nobilis, one of the false widow species. Males wander around looking for a mate, so can turn up in odd places. Tip him outside.
They can look a bit gruesome, but aren't aggressive, bites are really very rare & typically occur when they are inadvertantly crushed against the skin.
Where I live, 3 species of false widow are well established, they largely go unnoticed despite living around homes, workplaces & random man-made structures.