Robert Nelsen
About Robert Nelsen
Robert Nelsen is a co-founder and managing director of ARCH Venture Partners. Crunchbase lists him as co-founder from 1986 and as managing director from 1996. He has been involved in creating, sourcing, financing and developing more than 100 companies, according to the Parker Institute for Cancer Immunotherapy.
His X bio describes him as a company founder and venture capitalist focused on disruptive innovation, especially biotechnology and AI, and as an active angel in tech. His recent work includes founding Altos Laboratories and Karuna Therapeutics, creating Xaira Therapeutics, and founding National Resilience.
On AI, he posted on X that ARCH seeded and co-founded Netbot, an early internet shopping agent, and R2 Technology, a large-scale commercial healthcare AI company. He also wrote that ARCH was a seed and founding investor in Impinj and a seed investor and co-founder of Xaira. A PitchBook profile also lists him as co-founder of Project Prometheus and as an advisor to Mighty AI.
PitchBook records 15 personal investments, 6 current portfolio companies and 4 exits. The entries include Colossal (2022, 2023 and September 2025), Gameto (2022 and 2024), NobleAI (June 2022), Ligandal (May 2022), VICIS (2018) and Gali Health (a 2019 seed round).
Crunchbase lists 11 personal investments, including Neuralink, Katalyst, Elysium and Wisdo Health. It names Wisdo Health and VICIS as his exits. The databases differ in what they count, so treat these totals as approximate.
In August 2026, Astromech announced a $20M round led by Bob Nelsen. Peak 6, NeoGenesis Capital, Builders VC and CAZ Investments also took part. Astromech is a Dallas company spun out of Colossal Biosciences. It builds predictive AI models of biological change from evolutionary and multispecies genomic data. The round brought its total funding to $60M at a reported $3.8B valuation.
PitchBook shows a June 2024 investment in Stability AI. Its profile also credits him with initiating the reboot of Stability AI. It lists a June 2022 investment in NobleAI as well.
His public work centers on biotechnology and AI, with a strong overlap between the two. Astromech, NobleAI and Xaira are examples. Most of his recorded angel deals are in biotech and health, and PitchBook and Tracxn list the portfolio companies as US-based. He has not published a personal check size or a stated stage preference that we could confirm. His X posts argue for faster AI development and faster regulatory approval for rare disease treatments.
- Astromech: evolutionary biology AI company spun out of Colossal; led its $20M round in August 2026.
- Colossal Biosciences: genetic engineering company; PitchBook records his investments in 2022, 2023 and September 2025.
- Stability AI: generative AI company; PitchBook records an investment in June 2024.
- Gameto: biotechnology company; PitchBook records investments in 2022 and 2024.
- NobleAI: AI software company; PitchBook records an investment in June 2022.
- Wisdo Health: AI-powered social health platform; Crunchbase lists it as an exit.
- Xaira Therapeutics: AI drug discovery company he describes himself as seeding and co-founding.
- dallasinnovates.com/astromech-raises-20m-for-next-phase-of-bringing-ai
- pulse2.com/astromech-raises-20-million-at-3-8-billion-valuation
- app.dealroom.co/news/note/colossal-spinout-astromech-raises-20m-at-3-8
- pitchbook.com/profiles/investor/125099-20
- crunchbase.com/person/robert-t-nelsen
- x.com/rtnarch?lang=en
- x.com/rtnarch/status/1884402797476815303
- parkerici.org/person/robert-nelsen
Investing activity
Robert Nelsen appears in 1 AI deal tracked by the Lounge deals desk, rounds totalling $20M, and led 1 of them. The rounds are mostly Seed, with a median round size of $20M. The most recent is Astromech (Seed, $20M, Aug 2026).
Robert Nelsen most often invests alongside CAZ Investments, Builders VC, PEAK6 and NeoGenesis Capital, and the companies they back on Lounge are mostly in AI.
Deals
Frequently asked questions about Robert Nelsen
Who is Robert Nelsen?
Robert (Bob) Nelsen is a co-founder and managing director of ARCH Venture Partners. He also invests personally as an angel in biotech and AI companies.
Did Robert Nelsen lead the Astromech round?
Yes. Astromech announced in August 2026 that Bob Nelsen led its $20M round. Peak 6, NeoGenesis Capital, Builders VC and CAZ Investments also participated.
What AI companies has Robert Nelsen invested in?
Public records show Astromech, Stability AI (2024) and NobleAI (2022). On X he also cites Netbot, R2 Technology, Impinj and Xaira from his time at ARCH.
What is Robert Nelsen's angel check size?
He has not published a check size that we could confirm. Founders should not assume a figure from third-party database estimates.
What stage and sectors does Robert Nelsen back?
His public record centers on biotechnology and AI, mostly at the intersection of the two. His stage focus is not stated publicly.
How can founders contact Robert Nelsen?
He is active on X as @rtnarch. We found no personal website, and no LinkedIn profile we could confirm as his.
Is Robert Nelsen an angel investor?
Yes. Robert Nelsen invests personally as an angel.
What stage does Robert Nelsen invest at?
In the rounds tracked on Lounge, Robert Nelsen has invested at Seed, with a median round of $20M. Robert Nelsen led 1 of those rounds.
Who does Robert Nelsen co-invest with?
Robert Nelsen's most frequent co-investors on Lounge are CAZ Investments (1 deal), Builders VC (1 deal), PEAK6 (1 deal) and NeoGenesis Capital (1 deal).
How can founders reach Robert Nelsen?
Founders on Lounge can see Robert Nelsen's contact details in AI Investor Contacts (paid plans), check for a warm introduction through members who worked with them under Warm Paths, and add Robert Nelsen to their Investor Pipeline to track the conversation.