Altovar was a Lethean criminal.
In 2371, he visited Deep Space 9, and broke into the infirmary. He tried to steal several hundred milliliters of bio-mimetic gel, when Dr. Julian Bashir walked in on him. He telepathically attacked him, leaving Dr. Bashir in a coma for several hours. Altovar triggered a security alarm and was arrested by Odo soon after leaving the infirmary.
In the coma, Dr. Bashir dreamed that Altovar was hunting him and murdering the senior staff, who represented different aspects of his personality. (DS9: "Distant Voices")
Altovar was played by Victor Rivers.
His costume was sold off on the It's A Wrap! sale and auction
on eBay but named as a Kazon/Illyrian costume.  It was later sold again through eBay and the current owner found several name tags in this costume, parts worn by Tom Morga, Eric Hunter, Ken Wood, Mick T., Mickey Cassidy, Scott Hill, Jon Wright, David Winburn, and Tom Miller throughout
Deep Space Nine,