Eric Costello
Co-founder of Slack and Early Developer of Flickr
Data Confidence: 84% · Sources: 5 · Last Updated: Sep 18, 2026
- Net Worth ▲
- Estimated $50M – $300M
- Reach ▲
- 35.0M people
- Power ▲
- Costello directed core client and frontend software architecture for Slack, an enterprise collaboration tool deployed across millions of daily active users and over 80% of Fortune 100 companies.
- Influence ▲
- His frontend engineering work on Flickr and Slack helped establish key software design patterns for Web 2.0 photo sharing and modern real-time workplace messaging platforms.
- Network ▲
- He maintains significant tech founder and venture connections from co-founding companies alongside Stewart Butterfield and Cal Henderson, backed by top-tier venture firms including Accel and Andreessen Horowitz.
- Legacy ▲
- Costello is recognized as a foundational engineer on two major consumer and enterprise web products: Flickr, which defined early photo sharing, and Slack, which reshaped workplace communication globally.
- Trajectory ▲
- Stable — first assessment on record.
About
Eric Costello is an American software engineer and entrepreneur best known as a co-founder of Slack Technologies and an early core developer of Flickr. He began his software career at Ludicorp building Flickr, which was acquired by Yahoo in 2005. In 2009, he co-founded Tiny Speck alongside Stewart Butterfield, Cal Henderson, and Serguei Mourachov, serving as a lead frontend architect during the creation of Glitch and its subsequent pivot into Slack. Following Slack's $27.7 billion acquisition by Salesforce in 2021, Costello shifted away from software engineering to operate Fat Apple Farm, a regenerative agricultural venture in New York.
Known For
Co-founding workplace communication tool Slack and developing core user interface code for photo-sharing service Flickr.
Connections
Leadership & Employment
Similar Profiles
DatabricksTop National LevelData and artificial intelligence software company providing a cloud‑based lakehouse platform
Kalanithi MaranTop National LevelFounder and Chairman of Sun Group
Ananda KrishnanTop National LevelMalaysian entrepreneur, founder and chairperson of Usaha TegasSources
- Skyhighfarmcorroborated
- Fourweekmbacorroborated
- Britannicacorroborated
- Mediumcorroborated
- Buildingslackcorroborated