So we now know Rob will play Henry Costin and Sienna Miller will play Percy Fawcett's wife Nina Fawcett.

I previously posted a little info on Henry, here it is again incase you missed it.
He was a British corporal who in 1910 was bored with military life, he answered a newspaper advertisment that Fawcett had posted seeking an adventurous companion.
Short and stocky with a bold Kiplingesque moustache and heavily hooded eyes, Costin had proven to be Fawcett's most durable and capable assistant.
He was exceedingly fit, having been a gymnastics instructor in the Army, and was a world-class marksman.
One of his sons later on summed him up this way.
"A tough bugger who hated bullshit"