YES, Tony Stark a.k.a Sherlock Holmes a.k.a Robert Downey Jr. is going to sign-up with the Taiwanese Smartphone Giant HTC a 2 year global marketing campaign. The deal is probably worth $12 million. RD Jr. has been a great influence to the youth with his Tony Stark / Iron Man image, also Sherlock Holmes image was a powerful influence to many and in the recent times RD Jr. is one of the most renowned actor in the world.
The deal is still not official, but the actor will have the final creative say over the advertising campaign and noone else will play other than himself. Samsung & Apple always invests a large amount in advertising all over the world. The advertising has been a key factor in changing the game for Samsung against Apple. HTC might need to apply the same strategy for its new HTC One.
As far as I think RD Jr. is the right man to promote any product, because he is the coolest figure in the Hollywood right now. And a note : Robert Downey Jr. will not feature as Tony Stark or Sherlock Homes. Anyways he is the best for HTC right now.