UK 
United States
As the old adage goes, you are simply the sum of the company that you keep.
Yes, this is a generalisation, yet on many levels it’s quite true. If we spend our lives surrounded by people with ill intent, it’s likely that we ourselves will subconsciously start to justify such actions and even take those morals on board as our own. Similarly, if we’re surrounded by people with ambition, and the drive to achieve great things, we ourselves are more likely to achieve big things.
And this is compounded by your position. If your job title is senior, it’s important not just that you actualise the ambition to succeed and push the boundaries of your function, but also that you have others with whom to discuss key decisions and formulate plans. These could be seen as your key advisors. The Godfather had Tom Hagen as his (admittedly fictitious) right-hand man, Winston Churchill had Brendan Bracken and in the world of business, the legendary mogul Warren Buffett has Charlie Munger.
Backstabbing | 5 signs that you can't trust your co-workers
In the political sphere, such a group might be called a ‘brain trust’, which Wikipedia describes as ‘a group of close advisers’ who were ‘prized for their expertise in particular fields’.
