Now, back in the olden days, when there was no beer and no TV, and lots of people going crazy due to the lack of such luxury items, there was a man with a coat of many colours. This man, Joseph (aka David Tennant) had been given his coat by his father, because he was his favourite, which is understandable as Joseph (aka David Tennant) is very handsome, and is clearly the best at almost everything he does. However, Joseph (aka David Tennant) didn't get on well with his brothers, as they were jealous because none of them ever won awards, and one day they stole his coat and threw him into a pit before deciding that throwing him in a pit was a bit offensive to the pit in question as no one had asked it if it wished to have people thrown into it. Instead, they sold him to a big scary hairy man who took him to Egypt, where he was sold as a slave.
Now, as much as many of us would love to have Joseph (aka David Tennant) as a slave, RTD didn't particularly like this idea, as he wasn't a supporter of slavery. But Joseph (aka David Tennant) seemed to like his master, Potiphar (aka John Simm), and worked hard for him, until he was thrown in jail when Potiphar's wife (aka Freema Agyeman) tried to seduce him, and, upon failing, told Potiphar (aka John Simm) that Joseph (aka David Tennant) had tried to seduce her, because she sucks.
In jail, Joseph (aka David Tennant) prayed to RTD, and sang a nice little ditty about Closing Every Door. RTD stepped in and told the Pharaoh (aka Burn Gorman) that Joseph could sort out the dreams he'd been having that freaked him out a little, because they involved freaky canibal cows and lots of wheat.
Impressed by Joseph's ability to interpret dreams, as well as his good looks and brilliant acting skills, the Pharaoh made Joseph (aka David Tennant) his second in command, and gave him a sonic screwdriver, even though it hadn't been invented yet.