Strelka's father appeared only twice in the entire franchise, after which he was no longer mentioned. Strelka's father first appears in "Star Dogs". In the cartoon, Sirius has no physical form, so we see him as a constellation, and by the end he seems to us as a cluster of stars that very much resembles a dog. In the book "Belka and Strelka on the Moon", Sirius appears as a star fog and helps Belka and Strelka fly to the Moon.