Tower Ground Controller reported a taxing aircraft began to stray from its clearance and caused a critical ground conflict with a landing craft. The Controller states there were several calls to the wayward aircraft before contact was made.

Narrative

I taxied Aircraft X from FBO to Runway XXR for departure via taxiway 1 initially; to hold short of Runway YY. After receiving permission from Local Control 2 I continued their taxi with a left on Runway YY; crossing Runway XXC; and then a right on taxiway 2 to the full length. The above was readback correctly and it appeared Aircraft X was complying. Local Control 2 informed me of Aircraft X deviated from the aforementioned route and heading towards the intersection of Runway XXR and Runway YY where it appeared Aircraft Y was on landing roll-out. I pleaded with 'Aircraft X' to stop several times before adding the '[last part of their call sign]'. I later saw them make an unprompted 180 and begin heading back southbound on Runway ZZ; so I issued a left on taxiway 2. It definitely appeared Aircraft X had crossed the hold line for the intersecting runways but couldn't determine what their proximity was with the Aircraft Y. The Tower team saved the day today; especially the watchful eye of Local Controller 2. It definitely seems like 100% pilot error in this particular case. No recommendations.