Nathan Doctor

Nathan Doctor is the Founder and Managing Partner of Infinite Capital, a US firm that invests in what it calls generational innovation, with a focus on deep tech. Crunchbase lists his location as the United States. PEI lists the firm's office in West Palm Beach, Florida. MarketScreener lists his education as an undergraduate degree from the University of Southern California and study at USC Marshall School of Business.

Before investing full time, he built developer tools. He co-founded Codewars with Jake Hoffner in November 2012. It was prototyped at a Startup Weekend competition, and Wikipedia says it won first place there. Codewars is a community where developers train on programming exercises called kata. He later co-founded Qualified.io, a platform for assessing engineering skills, and served as its CEO. Per the Crunchbase bio, Qualified is used by Apple, Facebook, GE and Zoom, and Codewars has over 4 million engineers. Qualified now owns and operates Codewars. Crunchbase also lists ChainShot, an online education company where MarketScreener says he advised from 2018 to 2022, among his exits.

His own AngelList syndicate profile says he started in crypto in 2012, bought Bitcoin in 2013 and moved heavily into Ethereum in 2015. He launched Infinite Capital in 2018, according to MarketScreener and AngelList. CypherHunter says the firm was formerly named Synapse Capital. Crunchbase says he has founded 4 companies.

Per Crunchbase, Nathan Doctor has made 23 investments across 18 portfolio companies, with 3 exits, none by IPO. NFX Signal lists a larger set of 43 investments on record, so the counts differ by source. Crunchbase describes him as an active angel investor across tech sectors. Its latest listed investment is the Series A of H3X Technologies.

The Infinite Capital team page says the firm has been active across frontier technology for over a decade. It says its pre-consensus investments span electric vehicles, cryptocurrency, autonomous aerospace, satellites and physical AI. He also runs an AngelList syndicate. In it he says he syndicates select deals and that Infinite Capital gets first rights to allocations. The syndicate lists 336 unique LPs and a typical investment of $111k.

Public sources show AI as one of several themes in his portfolio, not the only one. NFX Signal lists Radical AI, with a seed round in July 2025, and Tracxn lists the same round. The AngelList syndicate profile names AI/ML and developer platforms among the markets he gravitates toward. Infinite Capital's own description includes physical AI.

The f4.fund firm profile, a third-party aggregator, lists robotics and physical AI companies in the firm's public portfolio: Apptronik (humanoid robotics), Mytra (warehouse robotics) and Extropic (thermodynamic computing chips). It also lists the crypto infrastructure projects Akash Network and Ocean Protocol. I could not find a public statement from Doctor on how he evaluates AI software startups specifically. Qualified's client list includes the Berkeley Center for AI, per his AngelList profile.

Stages: Infinite Capital invests from early concept to growth stage, according to f4.fund. NFX Signal tags his activity as seed and Series A across DeepTech, Space, Web3/Crypto and Education. His investments on record there include pre-seed, seed, Series A and Series C rounds.

Sectors: Infinite Capital describes itself as thesis-led and not a generalist. f4.fund lists its public portfolio as aerospace, autonomy and defense, nuclear and grid energy, robotics and physical AI, advanced computing, space and satellites, marine and electric vehicles, and crypto. His AngelList syndicate also lists fintech, education, real estate and micromobility.

Check size: Doctor has not published a personal check size that I could find. NFX Signal shows an investment range of $100K to $5.0M with a $1.5M sweet spot. That figure is NFX's listing and is not self-reported. His AngelList syndicate shows a typical investment of $111k. Geography: the disclosed portfolio is mostly US-based, with some international companies.

• H3X Technologies: electric propulsion company. NFX lists a seed in April 2021 and a Series A in August 2024. Crunchbase lists the Series A as his latest investment.
• Radical AI: AI company with a seed round in July 2025, listed by NFX Signal and Tracxn.
• Mach Industries: autonomous defense manufacturing. NFX Signal lists a Series C in June 2026.
• Medallion: NFX Signal lists a seed in May 2022 and a Series A in December 2023.
• Apptronik: humanoid robotics, listed in the Infinite Capital portfolio by f4.fund. The investment year is not stated.
• Mytra: warehouse robotics, listed in the Infinite Capital portfolio by f4.fund. The investment year is not stated.
• Extropic: thermodynamic computing chips, listed in the Infinite Capital portfolio by f4.fund. The investment year is not stated.
• Drosera: seed round in February 2024, listed by Tracxn as an Infinite Capital investment.
• D3: seed round in September 2023, listed by Tracxn as an Infinite Capital investment.

• crunchbase.com/person/nathan-doctor
• signal.nfx.com/investors/nathan-doctor
• venture.angellist.com/nathandoctor/syndicate
• f4.fund/firms/infinite-capital
• en.wikipedia.org/wiki/Codewars
• au.marketscreener.com/insider/NATHAN-DOCTOR-A2X9YU
• tracxn.com/d/venture-capital/infinitecapital/__TDQGT3TRbcOwxIVtrim1vjj
• cypherhunter.com/en/p/infinite-capital