Henry Cameron is an awesomesauce architect who is basically an older (and unluckier) version of Howard Roark. Cameron becomes Roark's mentor and helps him to kickstart his early career. But Cameron is far from an ideal mentor in many ways: he's an angry and bitter alcoholic who uses lots of tough-love tactics on Roark to make sure Roark is strong enough to meet his destiny.
Cameron, who dies early on in the story, serves as a sort of touchstone for Roark. The tragic life story of Cameron, who was a rockstar of the architecture world and then was beaten down by society, inspires Roark to continue on his own path and to fight the very system that kicked Cameron to the curb.
Cameron is also modeled after a real-life architect named Louis Sullivan, an innovative American architect who worked in the late-19th and early-20th century. Sullivan was considered the "father of the skyscraper," and his work was groundbreaking in the modernist architecture movement. That definitely sounds like Cameron, who "designed skyscrapers in straight, vertical lines, flaunting their steel and height" (1.3.66).