This was an extremely popular show in the UK, and followed on the hugely popular comic's Dennis the Menace. Season 1 of 26 episodes ran on the BBC and the popularity produced a second 26 episodes the following year.
NOT to be confused with the blonde boy of the same name in the USA, the UK version had a black and red striped shirt and spiked black hair.
I guess it was renamed Dennis and Gnasher to avoid the confusion when shown in the USA. Gnasher was Dennis's dog.
There were 52 episodes in all, but after a ten year gap rumor has it that he has been reworked, redesigned and looks like he may grace our screens again in the very near future. The original 52 were made by Tony Collingwood and the animation by Kieron Seamons. Well worth seeing again and again !