Boris Kropotkin is the father of both Ben and Didi, also the maternal grandfather of Tommy and Dil and the father-in law of Stu and Elaine. He, like his long-time wife Minka, comes from the "Old Country," so he says. This location was later revealed to be Russia. In the Rugrats Passover special, he mentions his wine glasses being from Smolensk, so it's possible that's the city he was originally from. He always talks about how horrible life was in the old country however Didi once revealed that he actually comes from a very well-off family. She then added "he wouldn't know a goat if it bit him in the face." He frequently gets into petty arguments with Minka over various issues, such as who will turn on the television, and why chocolate cake should be used at birthday parties, instead of carrot cake. He is also a wonderful storyteller, as he would often tell vivid stories about "monsters." He and Grandpa Lou are a lot alike in story-telling, their overactive imaginations with their stories, and were romantic with their wives.
Boris is a very eccentric, yet interesting man who is able to tell great stories. He argues often with Minka and, occasionally, Lou. He usually rambles on about his past experiences living in "the old country."
Boris is the grandfather of Tommy & Dil. As seen in "Toys In the Attic" he whispers to Tommy that he found Minka to be the most beautiful girl in the village and adores her cooking. Being Jewish, Boris and Minka embrace their religion well, sharing their faith with their extended family, including Angelica whom he also sees as his own grandchild. This is very evident in "A Rugrats Chanukah", when he sees Angelica crying, he carefully takes her from Schlomo and continues to hold and comforting her until she calms down.
It is also shown in "Toys In the Attic" that he and Minka keep various knick-knacks and antiques, most of which are broken by Tommy and Angelica. After which, they both faint, but later they hide all the antiques from the kids. He is seen in The Rugrats Movie, giving a goat for goat's milk to Didi when she is expecting Dil soon, and also helping Lou look after the babies when she goes into labor. He is seen in the beginning and end of Rugrats in Paris: The Movie, getting hit with cake by accident. Upon hearing Lou laugh at him, he starts a food fight by hitting him with cake.
Boris has peach skin, small black eyes, and a few hairs on his head. He is often shown wearing a green jacket and a white undershirt as well as blue jeans.
- In the early seasons of Rugrats, Boris was shown to have small eyes. However, in later seasons of Rugrats and All Grown Up!, Boris was shown to have larger eyes.
- Boris is revealed to be Russian-American in Chuckie Gets Skunked and Bad Blood.