Lester Freamon appears in Outland with Sean Connery.
It isn't sci-fi and it was a long, long time before The Wire, but Lester [Clarke Peters] turned up in a repeat of The Professionals on ITV 4 the other day. I even watched the closing credits, just to make sure it was him, he wasn't painstakingly constructing any miniature furniture though.
I knew nothing about him until I read his Wiki. He's a man of many talents, backing singer on Love and Affection by Joan Armatrading and Boogie Nights by Heatwave amongst other appearances on stage and screen both in the UK and the US, as well as being a friend of Ned Sherrin and writing Five Guys Named Moe for the stage. Bit of a polymath is Clarke.