Dragons' Den originally broadcast on BBC Two when the programme launched in 2005.
The channel was associated with factual, documentary and specialist entertainment programming, making it a natural home for a business-investment format. In each episode, entrepreneurs explain their products or companies while investors assess the opportunity and negotiate possible deals.
The show later became a major BBC brand and was also broadcast on BBC One for some periods. That later visibility can cause viewers to remember BBC One as the original channel, but the programme began on BBC Two.
Dragons' Den should also not be confused with the American adaptation Shark Tank. Both programmes descend from the same international format, while this question concerns the British series and its original BBC outlet.