Hermann Dennis Slikk (24 January 1910 - 24 May 2015) was Leopold, Leonard, and Leonidas Slikk's great-grandfather, 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.
In the Director's Cut version, after a much longer and arguably more intense fight, Hermann managed to get the upper hand; however, before he could deliver a killing blow, he was struck by a bolt of lightning, electrocuting him and allowing Leopold to throw him off the building.
Initially, Atarster intended Hermann to stay dead. However, after retconning episodes 126 and 127, he was brought back in the remade episodes. In Episode 126, Adolf Hitler exhumed Hermann's body and resurrected him. Hitler then sent him to Leopold's home to eliminate his grandson and great-grandson, once and for all. However, he was interrupted by his two grandsons, Harold and Gerald. Finally, his son Barry arrived and attempted to stop him, but failed. After subduing his son and two grandsons, Hermann kidnapped Leopold, Leonard, and Leonidas. In the following episode, Barry, Harold, and Gerald confronted Hermann in the exact same building he was thrown from. While Harold and Gerald fought their grandfather, Barry untied Leopold, Leonard, and Leonidas. The sextet fiercely fought the senior citizen; however, once again, Herman managed to get the upper hand, backing Leopold, Leonard and Leonidas into a corner. Just before he could finish them off, Hermann suffered a heart attack, causing him to stumble backwards. This gave Gerald the perfect opportunity to throw a hammer at his grandfather causing him to fall to his death once again, ending the tyranny of Hermann Dennis Slikk, once and for all.