Domino the Dalmatian, who is the constant companion of Heugh Battery Museum manager Diane Stephens, is celebrating his 14th birthday on Sunday, April 3.
Dog owners and animal lovers are invited to the Headland museum between 11am and 2pm for a series of events and activities with all proceeds to animal rescue charities.
Domino and his sister Poppy were rescue pups and organisers want to help other spotty dogs find happy homes and be well looked after.
There will be fun competitions, a dedicated dog photographer, raffles and a tombola.
Diane said: “Because Domino is 14 and getting on we just wanted to do something to mark a milestone birthday for him.
"We thought it was only going to be a small event but we have had an enormous response to it.
"Once again the people of Hartlepool have shown that they want to open their hearts to another cause.”
The competitions are free to enter and will look to find the dog with the Waggiest Tail at 11.30am and 1.30pm, and Best Treat Catcher at 12.30pm.
All dogs are welcome and visitors are asked for a donation on entry.
There will also be a small charge for the dog photographer.
Money raised on the day will be shared between DAS Dalmatians, which rehabilitates, rescues and rehomes Dalmatians in the UK, and Stray Aid, in County Durham, which takes in and rehomes animals from the Hartlepool area.