Charles Guillemet

Who they are

Charles Guillemet is CTO at Ledger — founded Ledger Donjon, the company's internal security research team, and graduated valedictorian in Cryptography and Security from ENSIMAG.

Person

Charles joined Ledger in December 2017 as its first Chief Security Officer, when the company was still an early-stage hardware crypto wallet maker — he has been there through its entire growth arc into a $1.3 billion company. His academic foundation is deep: valedictorian MSc in Cryptography and Security at ENSIMAG, plus a Master 2 in Security, Cryptology and Coding of Information Systems from Université Joseph Fourier. Before Ledger, he was a Technical Manager at CEA-LETI ITSEF (France's government-backed electronics and IT security lab), a Cryptosystems Design Expert at Tiempo S.A.S., and a Lecturer at ENSIMAG — a track that moved from academic cryptography into applied hardware security before landing in industry. He founded Ledger Donjon in 2017, Ledger's internal security research and evaluation team, which assesses the security of Ledger's own products — a rare move that embeds adversarial research inside the company that makes the thing. He was promoted to CTO (from CSO) and is now the technical face of the company, speaking at ETH Denver, Black Hat MEA, Proof of Talk, BTC Prague, and Blockworks events. Possibly — the through-line across everything is a conviction that security must be built in, not bolted on: from CEA-LETI's government lab work to founding an internal red team to now steering an AI security roadmap from the CTO seat.

Company

Ledger's most recent strategic moment is a shelved U.S. IPO: in May 2026 the company paused plans for a listing that had targeted a valuation over $4 billion, citing volatile market conditions and weak investor appetite for crypto listings, and is now exploring private capital raises instead — despite reporting record-breaking revenue in Q1 2026. To strengthen its U.S. institutional push it appointed John Andrews, former Circle executive, as CFO in March 2026 and opened a New York office focused on Ledger Enterprise. On the product side, Ledger released a 2026 AI security roadmap introducing hardware-anchored security for AI agents — phased features including Agent Identity, Agent Intents and Policies, and Proof of Human — alongside enterprise-grade on-premises hardware security solutions aimed at institutional crypto participants. Ledger has raised $575 million over 7 funding rounds, most recently a $109 million Series C extension in March 2023 at a $1.3 billion valuation.

Market

Ledger is the market leader in crypto hardware wallets, claiming roughly 20–25% of the retail hardware wallet market and securing approximately 20% of the world's cryptocurrency assets across more than 180 countries. Its main competitors are CertiK, MetaMask, and Casa, though Ledger has raised more total funding ($575 million) than most direct rivals in the segment. The sector is shaped by evolving U.S. and international regulation — including the CLARITY Act and stablecoin frameworks — geopolitical instability driving self-custody demand, and an accelerating institutional adoption wave that Ledger is explicitly trying to capture with its Enterprise platform and New York office.

Network

Guillemet reports to Pascal Gauthier, Ledger's Chairman and CEO, who has been his direct manager throughout his tenure. His peer executives include Quentin Ricomard (CFO) and Arnaud Prigent (Head of Product), with whom he collaborates on product direction. The newly appointed CFO John Andrews, the former Circle executive brought in for the U.S. expansion, is the latest addition to that leadership layer.

Pascal Gauthier· Chairman & CEO, Ledger
Quentin Ricomard· CFO, Ledger
Arnaud Prigent· Head of Product, Ledger
John Andrews· CFO (U.S. expansion lead), Ledger (appointed March 2026)

How they likely show up

Long tenure at Ledger (joined December 2017, now CTO) through multiple product generations and a near-IPO → thinks in multi-year arcs, not quarters.
Founded Ledger Donjon — an adversarial internal red team — rather than outsourcing security evaluation → builds institutions around problems rather than patching them.
Career path: government lab (CEA-LETI ITSEF) → cryptosystems design → academia (ENSIMAG lecturer) → industry operator → CTO → suggests he respects rigour and will spot hand-wavy security claims immediately.
Active on the conference circuit (Black Hat MEA, ETH Denver, BTC Prague, Proof of Talk, Blockworks) → comfortable being a public technical authority; responds well to substantive debate in an open setting.
Possibly — writes on Medium and LinkedIn on Web3 security and cryptography topics, suggesting he processes ideas by publishing them and may appreciate interlocutors who engage with specifics he has already put on record.

Conversation tips

→ Come with technical specifics — he has a valedictorian cryptography MSc and ran a government security lab; vague security claims will land badly.
→ Ask about Ledger Donjon by name — it's something he founded and it reflects a core conviction about how security should be organised; he'll have strong views on it.
→ Reference the AI security roadmap (Agent Identity, Agent Intents and Policies, Proof of Human) — it's the live product bet and likely where his current thinking is concentrated.
→ Don't conflate Ledger's hardware wallet roots with where he's steering the company; he's explicitly building toward a broader digital asset security platform and AI agent security infrastructure.
→ If you've read his Medium posts on cryptography or his LinkedIn writing on Web3 security, say so and name the piece — he'll know you've done the work.

Toolbox

Openers

Open on Ledger Donjon — he founded the internal red team in 2017 as CSO, which is an unusual structural bet: building adversarial security research inside the company whose products it evaluates. That tension is a natural conversation starter.
Reference the 2026 AI security roadmap — specifically the Proof of Human feature — because it's a pointed claim about what hardware-anchored security should do as AI agents proliferate; it's current, it's his technical agenda, and it invites debate.
Mention the paused IPO in the context of Q1 2026 record revenue: the company is making more money than ever and chose to stay private — that's an interesting strategic trade-off that sits at his level.

Discovery questions

When you designed the phased AI security roadmap — Agent Identity first, then Agent Intents and Policies, then Proof of Human — what was the threat model that forced that sequencing?
You founded Ledger Donjon as CSO before you became CTO — how does running an internal red team change the way you make product decisions from the CTO seat?
With the U.S. IPO on hold and Ledger deepening its institutional focus through the New York office and Enterprise platform, how does that shift what you're building on the hardware and firmware side?

Avoid

Don't open with generic blockchain-or-AI hype language — he has spent his career in applied cryptography and adversarial security research, and he speaks at Black Hat; imprecise claims about 'secure' systems will close the conversation down fast.

Make it yours