Individuals from various departments within your company may be involved in your R&D. While a developer or engineer is more likely to be involved in R&D than a marketing executive, you should always judge someone's involvement based on the eligible role they played in a qualifying project, not just their job title.
Overall key factors are who in your organisation was involved in those projects, what activities they performed and what percentage of their time they spent on R&D.
Our R&D Tax Credit calculator will estimate the tax relief you could claim from HMRC. You can perform R&D tax calculations for an SME, in profit or loss-making, or a large company.