Character Analysis
A Genial Guv'nor
Colonel Pickering is the closest thing Pygmalion has to a father figure. He's a sweet old chap, an expert in Sanskrit, and an all-around nice guy.
He and Higgins hit it off right away, and without his suggestion, the whole bet would have never happened. But that doesn't mean that he views Eliza as a mere robot, the way Higgins seems to. Quite the contrary: Eliza credits Pickering's gentlemanly ways for starting her transformation from flower girl to duchess, for truly making her feel like a lady:
LIZA [continuing] It was just like learning to dance in the fashionable way: there was nothing more than that in it. But do you know what began my real education?
PICKERING. What?
LIZA [stopping her work for a moment] Your calling me Miss Doolittle that day when I first came to Wimpole Street. That was the beginning of self-respect for me. [She resumes her stitching]. And there were a hundred little things you never noticed, because they came naturally to you. Things about standing up and taking off your hat and opening doors— (5.137-9)
Aww. He really is a good dude. He's the good cop to Higgins's bad cop (see "Character Roles" for more on this), the Sancho Panza to his Don Quixote.
A Sensitive Sidekick
That said, he still gets carried away sometimes: he gets all worked up about "inventing new Elizas," he forgets to congratulate her on her achievement, and he ignores the many warnings that he and Higgins receive.
Pickering really is the epitome of the sidekick. He serves a counterpoint for Higgins, someone Higgins can bounce remarks off. His presence also allows for the humorous, effusive bit of Eliza worship at the end of Act 3 (3.226-244). Ultimately, Pickering adds a little more spirit and little more kindness into the mix.