"might know him" is a correct and usable phrase in written English.
It is used to indicate a possibility. For example, "I thought I might know him from somewhere."
(You might know him now as Chuck).
You might know him as Boss Tweed.
The eyes have it; you feel as if you might know him.
Though you might know him better as Basshunter, the hunter of bass.
The more informed might know him as a middle-of-the-road singer-songwriter.
"Most Americans today might know him as a novelist if he hadn't been, in effect, blacklisted in the 1950s".
A lot of people might not know him but he's a very impressive player.
That means 50 million or so of the nation's 120 million households that might not know him will get their chance to meet El Perrero.
If you live anywhere near him though, you might just know him as a happy farmer in rural Massachusetts.
" 'What do you think we might know about him, or could find out that could discredit him?' " Mr. Low continued, according to Mr. Carle.
You might know part of him by looking at him, but you didn't know it all".
