Just a repost today on why Bob is your uncle.
It should be noted that there are several theories for this, and a new one is invented every week, but the standard line* is that it refers to the political career of Arthur Balfour. Balfour was Prime Minister of Great Britain from 1902 to 1905, which, given the size of the British Empire, made him pretty much the most powerful man in the world. However, it was not always thus. When he was first elected to parliament in 1874 he was considered a bit of a joke; and when he was suddenly made Chief Secretary for Ireland in 1887, everybody thought that it was rampant nepotism because the prime minister who promoted him was his uncle, Robert Cecil.
So, Balfour's easy success was down to the fact that Bob [Cecil] was his uncle.
As I said, there are a bunch of other theories, partially because the earliest written reference comes in 1931. However, if you wanted to know what Uncle Bob looked like, you should (probably) see the picture below.
*Despite what a citationless Wikipedia article may tell you.