The unseen and otherwise un-known brother of Nobby Nobbs. He is referenced in Guards! Guards! as the elder Nobbs brother who is thought to have been driven out of home by Sconner Nobbs to seek his fame and fortune in an unspecified Elsewhere. All we know of the elder Nobbs sibling is that by inference - the swamp dragon Errol was named after him because of a perceived resemblence - he is likely to have a long sad face and extremely flared nostrils.
Just behind the sketch of Maisie Nobbs that appears in Nanny Ogg's Cookbook, there is a mantlepiece of family iconographs: only Nobby and Sconner may be clearly identified. The mystery of the other two pictures, and whether or not either has anything to do with Errol, is yet to be determined.
The City Watch edition of the Discworld Diary includes a sample police report, written by Nobby, describing how he arrested his brother for attempting to steal his weapon collection during the night. Presumably this is Errol, maintaining the family tradition of pilferage from one's associates.