Cousin Mortimer is Basil's fiendish, sadistic cousin and The show's primary antagonist.
In the first series finale, he arrived and pretended to be kind and helpful to the local people but secretly he was stealing things and getting Basil into trouble. its revealed that His full name is Mortimer Trouble Brush.
In the second series, he was released from prison and he was still causing havoc.
In the third series he and Basil had to get along for 24 hours without fighting and arguing but it didn't seem to work. He also appeared at Basil's wedding when he was marrying evil Kelly Foxwell but in the end, Kelly liked Mortimer more than Basil. He returned in the Christmas special. He appeared in the fourth series in prison when he did something wrong that was unknown.
In the 2005 and 2006 Christmas specials.
His catchphrase is "Bang! Bang!", followed by the sound of two projectile ricochets.
- He is voiced by Don Austen who also voiced Bingo Brush.
- He was the first fox to be introduced.