Stephen O'Connor, Developer in Berlin, Germany
Stephen is available for hire
Hire Stephen

Stephen O'Connor

Verified Expert  in Engineering

iOS Developer

Berlin, Germany
Toptal Member Since
February 10, 2021

Stephen has specialized in iOS design and development since 2012. He has delivered a wide array of groundbreaking apps for clients, ranging from individuals to some of Germany's largest companies in the automotive and other sectors. The products he invents are exceptionally well-designed and usable because he understands customers' needs, collaborates closely with stakeholders, and responds to ongoing user feedback. Stephen values customer satisfaction, team harmony, integrity, and reliability.


Xcode, Objective-C, Swift, Postman, Slack, Affinity Photo, Terminal, Bash...
Wiwicon GmbH
App Design, UX Design, iOS UX Design, Objective-C, iOS, Xcode, Meetings...
Giveatoast GmbH
Xcode, Objective-C, PaintCode, Adobe Photoshop, Mobile Development, iOS SDK...




Preferred Environment

Xcode, Slack, Affinity Photo, Terminal, Postman, Swift, Objective-C, iOS, tvOS

The most amazing...

...thing I've done was to conceive, pitch, and create a whole new product category for a client, which resulted in having my name on a patent.

Work Experience

Senior iOS Developer

2012 - PRESENT
  • Developed countless apps for clients, as a lone developer or a member of a team, and for individual clients up to some of Germany's largest companies.
  • Tracked bugs and tasks, using tools such as Jira, Confluence, Toggl, and Trello.
  • Developed testing strategies and led app deployments and the Apple submission process.
  • Worked effectively in collaborative environments with distributed (remote) workspaces where communication skills were especially important.
  • Consulted on staffing and interview processes and participated in some interviews.
  • Proposed and designed features and UX concepts, sometimes acquiring new clients for the clients I was contracted to.
  • Created proprietary tools and pipelines (command-line tools and Bash scripts) that made UI-related and localization workflows more efficient while reducing dependencies on teammates.
  • Designed entire app features, from UX to software design, during some client engagements.
  • Leveraged many of the Core iOS frameworks on a regular basis, such as Core Data, Core Bluetooth, Core Animation, and AVFoundation (iOS native libraries).
  • Utilized established third-party technologies, such as Realm, Firebase, RestKit, and HockeyApp.
Technologies: Xcode, Objective-C, Swift, Postman, Slack, Affinity Photo, Terminal, Bash, Firebase, iOS, iOS Native Libraries, Firebase iOS SDK, Mobile Development, iOS SDK, Localization, Google Sheets API, Design Reviews, UX Design, Algorithms, Core MIDI, Model View ViewModel (MVVM), Carthage, Source Code Review, Prototyping, Git, CocoaPods, Core Bluetooth, SourceTree, Agile Software Development, Unit Testing, Research & Critical Thinking, Software Development, Core Data, REST API Clients, Feature Planning, Design, iOS UX Design, Mobile Apps

Head of Product Development

2013 - 2015
Wiwicon GmbH
  • Pioneered an entire product and pitched it successfully to the client, one of the largest manufacturers of lighting products in Germany, which was seeking, in part, to compete directly with the Philips Hue product.
  • Invented software UI components so novel in their approach that my name was present on the patent registration.
  • Interfaced and consulted with an associated team on which our work depended. Topics ranged from API design to product functionality considerations.
  • Developed the entire suite of iOS apps related to two products in Objective-C and was responsible for all aspects of their functionality and stability.
  • Served as a product owner concurrently with my role as iOS developer. I had the final word on what would be included in the product, oversaw the progress, and directed the tasks of three teammates—the designer, the intern, and sometimes the boss.
  • Attended regular meetings with the company's principal client, provided status updates, and directed creative ideation workshops.
  • Played a key role in staffing the team with the right people to enable our success.
  • Mastered essential concurrency paradigms, such as OperationQueue and Grand Central Dispatch, as well as data imports to Core Data contexts on background queues. Also required data communication at the socket level as opposed to HTTP.
Technologies: App Design, UX Design, iOS UX Design, Objective-C, iOS, Xcode, Meetings, Management, Design Reviews, Mobile Development, iOS SDK, iOS Native Libraries, Localization, Git, CocoaPods, Software Development, Core Data, Feature Planning, Design, Mobile Apps

Lead iOS Developer

2012 - 2013
Giveatoast GmbH
  • Developed the company's product, an iOS app, from the ground up, and was solely responsible for the app's success.
  • Worked in an Agile development team with standups and sprint boards.
  • Participated in high-level meetings about the product roadmap.
  • Advised decision-makers during the hiring process for new team members.
Technologies: Xcode, Objective-C, PaintCode, Adobe Photoshop, Mobile Development, iOS SDK, iOS Native Libraries, Design Reviews, Git, Software Development, Feature Planning, Design, Mobile Apps

Sound Artist

2005 - 2006
Electronic Arts
  • Developed an audio project, using the company's proprietary tools that would define how the video game's sound would function interactively with runtime inputs. The approach was very technical but the sound design seemed artistic.
  • Maintained legacy projects built with proprietary tools that pertained to play-by-play sports commentary.
  • Managed and categorized a large amount of audio data in Excel, and contributed to ideation of the next-generation tools for this purpose.
  • Edited a large number of audio voice samples, using typical tools of the day (such as Digidesign Pro Tools, Cubase, and VST), and categorized the samples according to proprietary formats.
Technologies: Cubase, ProTools, Microsoft Excel

Research Associate

2000 - 2002
Queen's University, Department of Physics
  • Investigated a very speculative research topic while employed as a student. Within weeks, using whatever means available, I achieved preliminary results that made it clear that we could apply for a grant.
  • Received a $200,000 research grant and served as the principal researcher on the topic of non-destructive testing of Tailor-welded Blanks, a component involved in the automotive manufacturing industry.
  • Held a postdoctoral research position as a bachelor's degree holder, which required special exceptions and arrangements.
  • Presented research findings to large groups at research conferences and published an article as the principal author.
  • Directed the tasks of summer student interns who were employed to assist me in my laboratory.
  • Developed rudimentary signal processing algorithms and designed and constructed the prototype testing apparatus, using a machine shop as required.
Technologies: LabVIEW, Research, Hardware Design, Instrumentation, Electronics, Public Speaking, Microsoft Excel

Roadtrip Music Player
A Swift-based app designed for people who go on long road trips and want to be able to quickly navigate their offline music collection with a bare minimum of user interaction required (as distracted driving is dangerous).

I designed and built the app completely solo. It involved heavy use of the AVFoundation and MediaPlayer frameworks; Core Animation APIs; implementation of in-app purchases; and interactions from remote controls, such as Apple headphones or the car steering wheel. The app is currently live on the App Store.


Swift, Objective-C, Java, Bash, Bash Script


Xcode, Slack, Terminal, Postman, Git, SourceTree, Affinity Photo, LabVIEW, Adobe Photoshop, Eclipse IDE, Sketch, Zeplin, PaintCode, Cubase, ProTools, Spreadsheets, Microsoft Excel


iOS, tvOS, MacOS, Firebase


Research & Critical Thinking, Analysis, Software Development, Mobile Apps, Prototyping, Design, Feature Planning, Mathematics, REST API Clients, AVFoundation, iOS UX Design, Writing & Editing, Source Code Review, Physics, Electronics, 3D Modeling, Algorithms, Game Design, Carthage, App Design, Meetings, Design Reviews, Localization, Research, Hardware Design, Instrumentation, Public Speaking


Core Data, Core Bluetooth, Core MIDI, iOS SDK


CocoaPods, Google Sheets API, Firebase iOS SDK, iOS Native Libraries


Model View ViewModel (MVVM), Agile Software Development, Mobile Development, Object-oriented Programming (OOP), Unit Testing, UX Design, Management

2007 - 2010

Bachelor's Degree in Computer Science

University of Applied Sciences (HTW Berlin) - Berlin, Germany

1997 - 2000

Bachelor's Degree in Physics

Queen's University - Kingston, Ontario, Canada

Collaboration That Works

How to Work with Toptal

Toptal matches you directly with global industry experts from our network in hours—not weeks or months.


Share your needs

Discuss your requirements and refine your scope in a call with a Toptal domain expert.

Choose your talent

Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.

Start your risk-free talent trial

Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.

Top talent is in high demand.

Start hiring