From: "Mal Duncan" page on Wikipedia.org website (http://en.wikipedia.org/wiki/Mal_Duncan; viewed 4 July 2007):
Publisher: DC Comics
First appearance: Teen Titans #26 (March-April 1970)
Created by: Robert Kanigher
Alter ego: Malcolm Arnold "Mal" Duncan
Affiliations: Doom Patrol, Teen Titans
Notable aliases: Guardian; Hornblower; Herald
Abilities: Generates multi-dimensional portals, and sonic blasts.
Mal Duncan, currently known as Vox, is a fictional character from DC Comics. He made his first appearance in Teen Titans #26 (March-April 1970).
Malcolm "Mal" Duncan saves the Teen Titans from a street gang called the Hell Hawks by beating their leader in a boxing match. Recruited by the Teen Titans, Mal feels unworthy due to his lack of abilities, and stows away on a rocket flight, which nearly costs him his life. After a time, Mal discovers a strength-enhancing exoskeleton, and the costume of the Guardian. Using these, he becomes the second Guardian.
After assuming the Guardian mantle, Mal fights Azrael - The Angel of Death. Believing it to be a hallucination, Mal is surprise to awaken with the mystical Gabriel's Horn. Having defeated Azrael, Mal is permitted to live, provided he never loses another fight. The horn grants Mal unspecified powers, whenever the odds are against him in battle. Armed with the horn, Mal assumes the name Hornblower.
Mal soon returns to his Guardian identity, claiming that too many people knew he was Hornblower. In truth, the Horn had been stolen. He marries Karen Beecher (Bumblebee), before moving to California. He is an accomplished jazz musician and owns a nightclub named "Gabriel's Horn".
Following the Crisis on Infinite Earths Mal's uncostumed adventures are unchanged. However, he never took the identity of Guardian, and the Gabriel's Horn is given a very different origin. While the other Titans are on a mission, Mal inadvertently releases an old villain, the Gargoyle (formerly Mr. Twister), from Limbo. He recaptures the villain, but finds the plans for a high-tech horn that would create spatial warps. With the help of Karen he builds the horn and takes the identity of Herald. After Mal learns that the horn weakens the boundaries between the mortal world and Limbo, he destroys it. He and Karen retire from super heroics, and move to California.
During the JLA/Titans event, Mal acquires a new Gabriel's Horn, and briefly joins the short-lived Titans LA. In the Titans Tomorrow storyline, the Mal of the alternate future becomes president of the Eastern United States.
When Doctor Light captures Green Arrow and demands to see the Titans, Mal rejoins the team for the last time. He then joins Troia to find out what's going on in space during Infinite Crisis.
Four weeks after disappearing in space, Mal is rescued from a Zeta Beam transport accident. His lungs and vocal cords were damaged after the Gabriel's Horn blew up in his face. Mal's body rejected the cybernetic grafting of parts from the Red Tornado until Steel used his Pseudocyte technology to permanently graft the parts into Mal's body.
A year after the events in Infinite Crisis, Mal has joined the Doom Patrol alongside his wife Bumblebee . Now going by the codename Vox, Mal speaks with a synthesized voice box which can create sonic blasts and open dimensional portals similar to the Gabriel Horn.
Formerly, his Gabriel Horn could open up multi-dimensional portals, and generate sonic blasts. He now relies on artificial lungs and voice box to achieve the same effects...
Herald first appears in Season 5 of Teen Titans "Calling All Titans." Unlike in the comic books, Herald wears a mask. He is voiced by Khary Payton. Blowing his horn allows him to open portals into other dimensions (or other places in his present dimension, including outer space). Herald is an honorary Titan, and fights off See-More and Warp. In doing so, his communicator is disabled.
From: "Jewish Comics Exhibit Notes" webpage, last updated 5 December 2004 (http://www.geocities.com/hadassahfink/comicexhnotes.htm; viewed 4 July 2007):
Teen Titans #45
After being buried under the rubble of a demolished building, Mal is met by Azrael, the angel of death. Mal demands a chance to fight for his life. After he defeats Azrael, Gabriel (who acted as referee) rewards Mal with a shofar (ram's horn) that can be used to make himself the equal of his opponents.