Carl Icahn said he saw no reason to keep demanding that Apple Inc increase its stock buyback plans.
Says valuations are rich and earnings at many companies are fueled by low borrowing costs.
The letter comes three weeks after demanding the iPhone maker take steps to boost its stock price.
Reduces his stake to 4.5% after making a total return of 457% in 14 months.
Gains came after Carl Icahn said he thinks the iPhone maker should do more to revive its stock price.
Board has told activist investor and Southeastern Asset Management they need to clarify the terms of their proposals.
Billionaire investor reportedly rebuffs board committee's request that he drop his threats and launch a formal bid for the company.
Carl Icahn and Blackstone are wooing Dell shareholders with more money.
Icahn, who is fighting Michael Dell's plan to take the company private, has entered a confidentiality agreement to access Dell's financial records.
Billionaire investor Carl Icahn wants Dell to remain a public company.
