There weren't a ton of Poison options in Generation I of Pokemon. But the available ones became staples in the games and the anime. The mix of those aspects has made some Pokemon on the Poison-type list very popular, regardless of their power. Of the handful of Poison-types, five made their name as popular picks in the franchise.
5 most popular Poison Pokemon from Kanto
#5 - Beedrill
Beedrill is not only a great pick in Generation I of Pokemon as a Poison-type, but it also serves as one of the cooler Bug-types in Generation I. It evolves from weedle and Kakuna, both of which players recognize as incredibly weak. However, once evolved, Beedrill is a useful addition ad looks a lot more intimidating than its previous forms.
Beedrill's is popular because of the addition of a Mega form for the Bee-like Pokemon. It looks interesting and is a powerful Poison-type.
#4 - Arbok
Arbok, or the very on the nose Cobra Pokemon spelt backwards, is another great Poison-type addition to Generation I. The purple King Kobra evolves from Ekans, which is also an on the nose snake.
Arbok is a decent tool on a team because it is a pure Poison-type Pokemon. Another aspect that cemented its popularity was its role in the anime—many associate Arbok with Team Rocket due to Jesse eventually evolving an Ekans into an Arbok.
#3 - Nidoking
The next few Poison-type Pokemon are all dual-type. Nidoking has a Ground and Poison dual type. The male Nidoking and the female Nidoqueen are similar in appearance and their respective Pokemon's third forms.
Nidoran is the first form of Nidoking, and it can be found fairly early on in Kanto. It was always one of the cooler looking Pokemon in Generation I. It is also a reliable addition to the team.
#2 - Gengar
For Ghost-type Pokemon, Gengar has been the poster child of the category for a long time, and is a fan favourite Pokemon from the Kanto region and in general.
Though it may be associated more with Ghost-type Pokemon, it still is a Poison-dual type, and its aesthetic has made it as popular as it is today, especially with a Mega form.
#1 - Venusaur
Gengar is debatably the most popular Poison-type in Kanto, but Venusaur outweighs it due to the status as a starter final form. The Kanto starters will always be some of the most iconic Pokemon in the franchise, and Bulbasaur's final form is hard to beat.