Who are the clients of investment bank trading divisions that act as market makers?

For market makers in the trading divisions of investment banks, who exactly are their clients? The companies in which they're setting bid/ask prices for on the stock exchange, or outside companies who are coming to Goldman for money? Or both? I guess what I'm trying to ask is, do the investment banks actually get hired by companies on the stock exchange as market makers and to set bid/ask prices? Or do they just perform this task to make money for clients coming to them in need of capital?