Councilor Dumah was a B'omar male who assisted Chancellor Gaumen in negotiations with the USS Voyager for passage through B'omar space in 2374.
The B'omar were very xenophobic, and Dumah laid down many restrictions on Voyager – they could not exceed warp 3, they had to avoid the planets and colonies of the B'omar, and they had to stop for seventeen inspections.
Dumah later piloted a patrol ship and tried to stop Seven of Nine who believed she was called back to the Borg Collective and stole a shuttle from Voyager. But Dumah's patrol ship was attacked by Seven and unable to stop her. (VOY: "The Raven")
Dumah was played by actor Mickey Cottrell who filmed his scenes on Monday 21 July 1997 and Tuesday 22 July 1997 on Paramount Stage 8.
His costume was later sold off on the It's A Wrap! sale and auction on eBay and, according to the costume tag, was also worn partially by Gaumen actor Richard J. Zobel, Jr.. [1](X)
Dumah's name comes from the script. He was named by Bryan Fuller who took the name from a book of angels; he named the Star Trek character after the angel Dumah. (Information from Larry Nemecek)