Tesla chair Robyn Denholm has justified her decision to offer Elon Musk $1tn in stock, calling him a “unique” chief executive who must put in superhuman effort and achieve “impossible things” to receive the historic award.

Last week, Tesla’s board proposed a pay package that would grant Musk 12 per cent of the electric-vehicle maker’s shares if over the next decade he can octuple its valuation to $8.5tn, boost earnings 24-fold and sell millions more cars and robots. But achieving even half of the incremental targets could make him the world’s first trillionaire.

“In order to achieve the aspirational goals that we have put in place, he will have to put in time, energy and effort beyond what most humans can do,” Denholm said in an interview with the Financial Times in Palo Alto ahead of a critical shareholder vote on Musk’s pay in November.