Cerberus Langarm

Cerberus Langarm worked for the Ministry of Magic as an Department of Magical Law Enforcement officer tasked with, presumably among other things, liaison between his own Department and the Department for the Regulation and Control of Magical Creatures and would pass on intelligence regarding nasty run-ins between dangerous magical creatures and humans to the Beast Division. Also charged with attending to the legal aspect as well as ensuring the safety of his the general public, he would occasionally accompany his co-workers and secure the area in which the beast in question is believed to be located to prevent civilians from entering it and thus avoid further injuries.

He helped investigate the attack on Chudley Cannons' keeper Gordon Horton.

Behind the scenes

 * As the most common usage of the term 'officer' in everyday use is that of referring to a policeman or policewoman, it can perhaps be reasoned that Langarm is a member of the Magical Law Enforcement Patrol, as they can be considered to be roughly the wizarding equivalent.
 * His last name might be a pun on "long arm", as in the idiom long arm of the law, used to refer to the police.

Notes and references
Cerberus Langarm