Mark Essel

Tech Co-founder Citizen, Welcome, Startup Tech Consultant

As the technical Co-founder of Citizen, Mark led the engineering team and designed their backend services. Following a consulting period, he served as a Tech Co-founder at Welcome, lead the development of their personalization system, itinerary planner, and other backend systems. After Welcome was acquired and supporting that transition, he has returned to consulting.

In his first career, Mark delivered multiple large-scale sensor simulations and algorithms for intelligence target detection, trac…

Mark Essel


  • Concierge: Realtime Recommendation Engine

    Concierge: Realtime Recommendation Engine

    This was a system I built while serving as co-founder at It was built to support immediate personalized results to users who engaged with our mobile clients. Signals were passed via client in batched updates to our backend. There we persisted meaningful actions, and forwarded events through redis via pubsub to concierge nodes. Each concierge instance was capable of ingesting a recent snapshot (hourly trained) and delta training to the most recent data while receiving live updates. Interval training was performed offline via cron jobs in a worker process hourly. The data ingestion rate was controlled by a timeout setting on each worker in the pubsub reader await asyncio.sleep(0.01). This architecture is only feasible for ingestion rates that can be managed by the resources of a given worker (for massive systems the event space would need to be partitioned further).

    This was all made possible by building on incredible techonologies like, redis, and our aws based nomad architecture.


  • Tek Horizons

    Tek Horizons


    Sep 2017 - Present

    Solo tech consultancy, fractional CTO, and independent contributor

    • Providing technical leadership and delivering custom backend engineering systems
  • Dorsia


    Senior Backend Engineer

    May 2023 - Feb 2024

    Dorsia’s mission is to transform the economy and experience of hospitality through technology

    • Enhanced frictionless tracking, rebooted onboarding logic, general API support
  • Welcome



    Oct 2017 - May 2023

    A Smart City Guide Discover the best places from your favorite people. Welcome is your new personalized city guide. It's powered by friends and experts — and made smart by a real time AI.

    • Developed interactive itineraries based on social and personalized signals
    • Developed and deployed ML tools to support user travel through personalization
  • Citizen


    Technical Co-founder

    Nov 2015 - Sep 2017

    • Designed, Implemented, and Deployed API & backend live video streaming architecture, geo push services Managed engineering goals and timelines
    • Lead Backend Engineer
  • Vimeo


    Principal Engineer

    Mar 2014 - Nov 2015

    • Design, Optimize, & Enhance backend video processing architecture (tools, dataflow, encoding)
    • Mobile Application Development (iOS/Swift) + OpenGL frame rendering
  • Fast Society (Acquired by Vimeo)

    Fast Society (Acquired by Vimeo)

    Chief of Research & Development

    Apr 2012 - Mar 2014

    • Architect and Optimize backend video processing architecture (tools, dataflow, encoding)
    • Port JavaScript animations to C++ (nodejs modules)
    • Migrate C++ effects to OpenCL/OpenGL
    • Designing novel animations/effects
    • Leveraging OS image/video libraries Cairo, GraphicsMagick, opencv, ffmpeg
    • Video encoding and streaming (ffmpeg)
    • Optimize utilization of cloud infrastructure
    • Support scaling the backend architecture
    • Continuous Testing and Deployment
    • Enhance platform stability
  • Victus Media

    Co-Founder (CEO)

    Oct 2009 - Oct 2010

    A business based on connecting social sharing with intelligent advertising, and powerful two way search

    • Co-founder/Product Lead
    • Ruby on Rails
    • Ngram Entity Extraction + Contextual Advertising
  • Photon Research Associates (Acquired by Raytheon)

    Sr. Staff Scientist

    Jan 1996 - Apr 2012

    Aerospace consultancy/tech company

    • Optimal Protein Data Structure Search (PDB)
    • Hyperspectral Simulations and Detection
    • Airborne + Space Based Sensors
    • 2D & 3D Tracking Systems
    • Detection/Discrimination Algorithms
    • SBIRS High/Low Simulations
    • Simulations, Systems, and Algorithm Design primarily using C++
  • Stony Brook University

    Stony Brook University

    MS Electrical Engineering

    Sep 1995 - May 1997

    • Graduate School
  • Stony Brook University

    Stony Brook University

    BS Physics

    Sep 1991 - May 1995

    • Undergrad

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