Hermann Dennis Slikk (24 January 1910 - 24 May 2015) was Leopold, Leonard, and Leonidas Slikk's great grandpa, Harold & Gerald Slikk's grandfather, and he was also the father of Barry Slikk. So far, he has only appeared in Atarster's AGK Series.
In Episode 50: AGK's Great-Grandfather (Episode 125 in Dipsy57_YT's AGK Series), Hermann kidnaps Harold and took him to the largest building in the city. Meanwhile, at Leopold's house, the boys watched the news about their father's kidnapping, and traveled downtown to stop him. Leopold climbed to the top of the building, and confronted his great-grandfather. After the fight, police helicopters sent by Leonard arrived at the building and they started shooting at Hermann. Hermann used his sledgehammer to hit one of the helicopters, and eventually destroys it. However, Hermann eventually collapsed to the floor due to his injuries, leading to Leopold throwing him off the building to his death. Afterwards, Leopold untied his father and the family returned home, relived.
Hermann is never seen again after this.