Bob Lee was an American tech entrepreneur and software engineer best known as the creator of Cash App and a former chief technology officer (CTO) at Square, who later served as chief product officer at the crypto-focused company MobileCoin.

Quick Scoop: Who was Bob Lee?

  • Full name: Bob Lee, often nicknamed “Crazy Bob” in tech circles.
  • Born: December 20, 1979.
  • Died: April 4, 2023, after being fatally stabbed in San Francisco, an event that drew huge attention in Silicon Valley and online forums.
  • Known for:
    • Helping create and launch Cash App at Square.
* Serving as CTO of Square, contributing to its payment technology stack.

* Serving as chief product officer at MobileCoin, a privacy-focused cryptocurrency project.

Tech career and impact

  • At Square, Lee was a key engineering leader during the period when the company expanded from card readers into broader payments and P2P products like Cash App, which became one of the most widely used money-transfer apps in the U.S.
  • Earlier in his career he was known as a strong systems and security engineer; for example, in 2001 he released a free tool to defend Microsoft IIS servers from the Code Red worm during a major internet security incident.
  • Friends and colleagues often described him as an energetic, highly social coder-turned-founder who moved easily between hardcore engineering and startup networking events.

His death and later legal developments

  • Lee was stabbed multiple times in San Francisco on April 4, 2023, and died shortly afterward, which triggered a wave of commentary about crime in the city and safety in tech hubs.
  • Police later arrested another tech entrepreneur, Nima Momeni, who knew Lee socially; prosecutors charged Momeni with murder, arguing the killing followed a personal dispute rather than a random street attack.
  • In late 2024, a jury convicted Momeni of second-degree murder; he was acquitted of first-degree murder but now faces a potential sentence ranging from 16 years to life in prison.
  • As of 2025, Lee’s family has also filed a civil lawsuit against Momeni and others connected to the case, keeping the story in the news and in ongoing forum discussions.

How people talk about him online

  • In tech forums and news comment sections, discussions around “who was Bob Lee” often mix:
    • Respect for his role in building Cash App and modern payment tools.
* Debates about crime and public safety in San Francisco after his killing.

* Curiosity and speculation about his personal life and the social scene that linked him to his killer, based on trial reporting and long-form features.
  • Over time, the conversation has shifted from the initial shock toward:
    • Legal outcomes (Momeni’s conviction, appeals, and sentencing).
    • The Lee family’s civil actions and their push for accountability.

Mini timeline

  1. 1979 – Bob Lee is born in the U.S.
  1. Early 2000s – Gains visibility in security and systems engineering, including work related to the Code Red worm.
  1. 2010s – Rises at Square, becomes CTO, and plays a central role in building Cash App.
  1. Later 2010s–early 2020s – Joins MobileCoin as chief product officer and continues working in fintech and crypto.
  1. April 4, 2023 – Fatally stabbed in San Francisco.
  1. 2023–2025 – Arrest, trial, and conviction of Nima Momeni; ongoing appeals and a civil suit by Lee’s family keep the case in the headlines and in forum debates.

TL;DR: Bob Lee was a prominent Silicon Valley engineer and entrepreneur, best known as the creator of Cash App and former CTO of Square, whose 2023 stabbing death in San Francisco led to a high-profile murder case and ongoing public discussion about tech culture and urban safety.

Information gathered from public forums or data available on the internet and portrayed here.