Silent person

The silent people were a species of metamorphs who lived in near-total isolation.

Biology
The silent people were capable of changing their form. Normally, they were disembodied, with only the barest of senses and limited ability to manipulate things. In order to mate, they also took on a humanoid form. This humanoid form was black, with flecks of silver around the body. The head was featureless except for a wide mouth and two glowing red eyes. The silent people were also able to modify other matter, fusing things together.

The silent person who came to to Cardiff was also capable of projecting its emotions (namely, its feelings of loneliness), speak with words and travel through the Rift, but only with difficulties. (TWN: Into the Silence)

History
The silent people lived on the Silent Planet, completely isolated from each other. Though scientists had come to study them, they were unable to contact them or communicate.

At some point in its history, the Rift opened a connection from the Silent Planet to 21st century Cardiff. This connection was noticed by an individual with a mental illness, namely one who wanted contact with others. It was able to force its way through the Rift and was attracted by the sounds and emotions it felt. Though it enjoyed the music, especially the singing for the Welsh Amateur Operatic Contest, it was unable to understand the concept behind it. Instead, it hunted down the singers and removed their vocal cords, trying to attach them to itself so it could sing. In time, it killed Richard Greenwood, Barry Llewelyn, Karen Peters, Maria Bruno and Ben Pritchard.

With the high death rate and the connection to the Contest, the rate of singing dropped, allowing Torchwood Three to track it more easily. In the first attempt, Ianto Jones and Drew Powell were used as bait, but they were unable to react quickly enough and Ben was severely injured. For their second attempt, they were able to get a minute of silence for Maria Bruno, allowing Ianto to be the only possible target. Instead, the silent person went after Ryan Scott, an autistic child who sang constantly. Captain Jack Harkness was eventually able to convince it to completely fuse with Ryan, who wanted isolation as much as the silent person wanted companionship. With that, they were pulled back through the Rift to the Silent Planet. (TWN: Into the Silence)