BlackRock (BLK) is the largest asset manager in the world, with $4.525 trillion in total assets under management AUM and clients in more than 100 countries. The AUM generates Fee Revenues of around $5.5 billion a year. Product diversity and a heavier concentration in the institutional channel have traditionally provided BlackRock with a much “stickier” set of assets, or a propensity not to migrate to competitors, than its peers. BlackRock's well diversified product mix makes it neutral to shifts among asset classes and investment strategies, limiting the impact that market swings and/or withdrawals from individual asset classes or investment styles can have on its AUM. For example, BLK offers the iShare brand ETFs in Equity, Fixed Income, International and Multi-Asset allocations. 

Many think BLK is mainly a retail-focused firm, but they offer specialized services for the following categories of customers:

In its most recent investor's presentation, the company offers an interesting breakdown of its client base:

Source: blackrock.com

The company outlines its philosophy on its website:

“BlackRock is the world's largest asset manager, and our business is investing on behalf of our clients, from large institutions to the parents and grandparents, the doctors and teachers who entrust their savings to us.  We work only for our clients—period. Our promise is to offer them the clearest thinking about what to do with their money and the products and services they need to secure a better financial future. That is why investors of all kinds entrust us with trillions of dollars, and it is why companies, institutions and global governments come to us for help meeting their biggest financial challenges.”