"He has made all the money he wanted to from his ancestors, and has no
aspiration to work for."
This is a bias and is likely skewing or prejudicing your assessment of him. Try to remove that from your thinking the best you can.
Everyone has unproductive time at work. Estimates range from 40% to 75% productivity in any given full day of work.
So the first question you should ask yourself is your perception of his wealth and the observed unproductive time linked.
That said, it comes to something measurable. If you can show he is behind his peers in performance with measurable results, then have that cometojesus meeting and set a recovery plan with, again, measurable milestones. If he fails, send him packing.
"How did this answer the question?" EDIT: First, I am challenging the OP in taking a look at the possible bias that could be skewing the his/her initial assessment of the employee. Bringing up someone's wealth is not relevant and is a sign, to me, of a potential interfering bias. Second, since the employee is near being fired, the ONLY motivators of any value at this stage is the basic, bare bones milestones in a recovery plan. Meet these or leave. That's it. The finer points of motivation, those that promote intrinsic desire to achieve--autonomy, mastery, and purpose--are things down the road. This guy just needs to keep his job if he wants it.