The specifics of what an investor might try to look for may vary depending on whether the startup is, say, a daily deals play, a chip company, a mobile app, or a genomics startup.

In general, here are the key things being examined with respect to a technical co-founder. Different investors might give differing weightages to these factors:

(1) Technical vision for the product and their ability to actually deliver on it.

(2) The unique technical/scientific insight they bring to the product and/or what are the confluence of technical factors/trends/improvements they are capitalizing upon.

(3) What have they done prior to the startup that can provide some degree of confidence for item #1? (e.g., companies they have worked at, schools they have graduated or dropped out of, etc.)

(4) What are the dynamics between the technical and non-technical cofounders? Have they successfully worked together before in another intense setting? If not, are there signs that can work together now?

(5) Will the technical co-founder be able to attract, scale up, and manage the tech team? (Many VC firms are increasingly helping out their portfolio companies in attracting top tech talent these days.)

If there is interest in continuing discussions with the co-founders, a VC firm will often have CTOs from their existing or past portfolio companies have detailed discussions with the technical co-founders to get deeper insights especially on items #1 and #2 mentioned above.