The Wire co-star Clarke Peters told BBC Radio 4's Today programme: "He was a generous actor. It wasn't me, me, me. It was us, us, us."
Film-maker Spike Lee described Williams on Instagram as "his brother" and said he "was shook" at the news.
The Wire creator David Simon said he was "a fine man and a rare talent".
Alongside a picture of Williams, Simon wrote that he was "too gutted right now to say all that ought to be said", adding: "On our journey together he always deserved the best words. And today those words won't come."
