The eight lifecycle stages of a buyer's journey in HubSpot are: Subscriber, Lead, Marketing Qualified Lead (MQL), Sales Qualified Lead (SQL), Opportunity, Customer, Evangelist, and Other. These stages help track leads throughout marketing and sales processes and develop effective lead management strategies. Each stage has distinct characteristics and behaviors that define its position in the buyer's journey. The lifecycle stages are not set by HubSpot but rather defined by each company to suit their needs. Marketing is typically responsible for Subscribers, Leads, and MQLs, while Sales is responsible for SQLs and Opportunities. Aligning marketing and sales teams through service level agreements (SLAs) ensures no leads slip through the cracks.